Maven clean install problem

Hi I cloned the repo with sources, and typed `maven clean install` in root folder. That is my error output:

```bash
$ mvn clean install -e
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] Computing target platform for MavenProject: com.gwtplugins.eclipse:com.gwtplugins.eclipse.suite.v3.feature:3.0.0-SNAPSHOT @ F:\AnotherProjects\gwt-eclipse-plugin\features\com.gwtplugins.eclipse.suite.v3.feature\pom.xml
[INFO] Adding repository http://download.eclipse.org/cbi/updates/license
[ERROR] Failed to resolve target definition F:\AnotherProjects\gwt-eclipse-plugin\eclipse\mars\gwt-eclipse-mars.target: Failed to load p2 metadata repository from location http://download.eclipse.org/cbi/updates/license: HTTP Proxy Authentication Required: http://download.eclipse.org/cbi/updates/license/content.xml -> [Help 1]
org.apache.maven.MavenExecutionException: Failed to resolve target definition F:\AnotherProjects\gwt-eclipse-plugin\eclipse\mars\gwt-eclipse-mars.target: Failed to load p2 metadata repository from location http://download.eclipse.org/cbi/updates/license
at org.eclipse.tycho.core.maven.TychoMavenLifecycleParticipant.afterProjectsRead(TychoMavenLifecycleParticipant.java:100)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:266)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.eclipse.tycho.core.shared.BuildFailureException: Failed to resolve target definition F:\AnotherProjects\gwt-eclipse-plugin\eclipse\mars\gwt-eclipse-mars.target: Failed to load p2 metadata repository from location http://download.eclipse.org/cbi/updates/license
at org.eclipse.tycho.p2.target.TargetDefinitionResolver.resolveContent(TargetDefinitionResolver.java:99)
at org.eclipse.tycho.p2.target.TargetDefinitionResolverService.resolveFromArguments(TargetDefinitionResolverService.java:70)
at org.eclipse.tycho.p2.target.TargetDefinitionResolverService.getTargetDefinitionContent(TargetDefinitionResolverService.java:60)
at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.resolveTargetDefinitions(TargetPlatformFactoryImpl.java:214)
at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.createTargetPlatform(TargetPlatformFactoryImpl.java:155)
at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.createTargetPlatform(TargetPlatformFactoryImpl.java:128)
at org.eclipse.tycho.p2.target.TargetPlatformFactoryImpl.createTargetPlatform(TargetPlatformFactoryImpl.java:1)
at org.eclipse.tycho.p2.manager.ReactorRepositoryManagerImpl.computePreliminaryTargetPlatform(ReactorRepositoryManagerImpl.java:84)
at org.eclipse.tycho.p2.resolver.P2DependencyResolver.computePreliminaryTargetPlatform(P2DependencyResolver.java:223)
at org.eclipse.tycho.core.resolver.DefaultTychoResolver.resolveProject(DefaultTychoResolver.java:109)
at org.eclipse.tycho.core.maven.TychoMavenLifecycleParticipant.afterProjectsRead(TychoMavenLifecycleParticipant.java:95)
... 14 more
Caused by: org.eclipse.tycho.p2.target.facade.TargetDefinitionResolutionException: Failed to load p2 metadata repository from location http://download.eclipse.org/cbi/updates/license
at org.eclipse.tycho.p2.target.TargetDefinitionResolver$LoadedIULocation.loadRepository(TargetDefinitionResolver.java:290)
at org.eclipse.tycho.p2.target.TargetDefinitionResolver$LoadedIULocation.(TargetDefinitionResolver.java:282)
at org.eclipse.tycho.p2.target.TargetDefinitionResolver$ResolverRun.addLocation(TargetDefinitionResolver.java:154)
at org.eclipse.tycho.p2.target.TargetDefinitionResolver.resolveContentWithExceptions(TargetDefinitionResolver.java:121)
at org.eclipse.tycho.p2.target.TargetDefinitionResolver.resolveContent(TargetDefinitionResolver.java:94)
... 24 more
Caused by: org.eclipse.equinox.p2.core.ProvisionException: HTTP Proxy Authentication Required: http://download.eclipse.org/cbi/updates/license/content.xml
at org.eclipse.equinox.internal.p2.repository.CacheManager.createCache(CacheManager.java:243)
at org.eclipse.tycho.p2.remote.RemoteRepositoryCacheManager.createCache(RemoteRepositoryCacheManager.java:67)
at org.eclipse.equinox.internal.p2.metadata.repository.SimpleMetadataRepositoryFactory.getLocalFile(SimpleMetadataRepositoryFactory.java:66)
at org.eclipse.equinox.internal.p2.metadata.repository.SimpleMetadataRepositoryFactory.load(SimpleMetadataRepositoryFactory.java:88)
at org.eclipse.equinox.internal.p2.metadata.repository.MetadataRepositoryManager.factoryLoad(MetadataRepositoryManager.java:57)
at org.eclipse.equinox.internal.p2.repository.helpers.AbstractRepositoryManager.loadRepository(AbstractRepositoryManager.java:768)
at org.eclipse.equinox.internal.p2.repository.helpers.AbstractRepositoryManager.loadRepository(AbstractRepositoryManager.java:668)
at org.eclipse.equinox.internal.p2.metadata.repository.MetadataRepositoryManager.loadRepository(MetadataRepositoryManager.java:96)
at org.eclipse.tycho.p2.remote.RemoteMetadataRepositoryManager.loadRepository(RemoteMetadataRepositoryManager.java:61)
at org.eclipse.tycho.p2.remote.RemoteMetadataRepositoryManager.loadRepository(RemoteMetadataRepositoryManager.java:53)
at org.eclipse.tycho.p2.target.TargetDefinitionResolver$LoadedIULocation.loadRepository(TargetDefinitionResolver.java:288)
... 28 more
Caused by: org.eclipse.ecf.filetransfer.BrowseFileTransferException: Proxy Authentication Required
at org.eclipse.ecf.provider.filetransfer.httpclient4.HttpClientFileSystemBrowser.runRequest(HttpClientFileSystemBrowser.java:291)
at org.eclipse.ecf.provider.filetransfer.browse.AbstractFileSystemBrowser$DirectoryJob.run(AbstractFileSystemBrowser.java:69)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)
[ERROR]
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MavenExecutionException

```

ルートフォルダーで `mvn clean install` コマンドを再現し、`eclipse/mars/gwt-eclipse-mars.target`、特にその `http://download.eclipse.org/cbi/updates/license` location を調査します。失敗がプロキシ認証に固有のものか、プロジェクト設定に固有のものかを判断し、再現可能なビルド結果を記録します。

索引モデルが issue の本文から書いたものです。