Fix class loader leak

_From [crazyboblee](https://code.google.com/u/114815478402472606661/) on June 30, 2010 21:52:15_

The OSGi tests failed for me:

    [junit] There were 3 errors:
    [junit] 1) testProxyClassUnloading(com.googlecode.guice.BytecodeGenTest)java.lang.OutOfMemoryError: Java heap space
    [junit] 2) testProxyClassUnloading(com.googlecode.guice.BytecodeGenTest)java.lang.OutOfMemoryError: Java heap space
    [junit] 3) testGuiceWorksInOSGiContainer(com.googlecode.guice.OSGiContainerTest)org.osgi.framework.BundleException: Activator start error in bundle osgitests [4].
    [junit]         at org.apache.felix.framework.Felix.activateBundle(Felix.java:1807)
    [junit]         at org.apache.felix.framework.Felix.startBundle(Felix.java:1682)
    [junit]         at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:905)
    [junit]         at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:892)
    [junit]         at com.googlecode.guice.OSGiContainerTest.testGuiceWorksInOSGiContainer(OSGiContainerTest.java:136)
    [junit]         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [junit]         at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    [junit]         at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    [junit] Caused by: com.google.inject.internal.ComputationException: com.google.inject.internal.ComputationException: com.google.inject.internal.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null
    [junit]         at com.google.inject.internal.MapMaker$StrategyImpl.compute(MapMaker.java:553)
    [junit]         at com.google.inject.internal.MapMaker$StrategyImpl.compute(MapMaker.java:419)
    [junit]         at com.google.inject.internal.CustomConcurrentHashMap$ComputingImpl.get(CustomConcurrentHashMap.java:2041)
    [junit]         at com.google.inject.internal.FailableCache.get(FailableCache.java:46)
    [junit]         at com.google.inject.internal.ConstructorInjectorStore.get(ConstructorInjectorStore.java:48)
    [junit]         at com.google.inject.internal.ConstructorBindingImpl.initialize(ConstructorBindingImpl.java:113)
    [junit]         at com.google.inject.internal.InjectorImpl.initializeJitBinding(InjectorImpl.java:382)
    [junit]         at com.google.inject.internal.InjectorImpl.createJustInTimeBinding(InjectorImpl.java:636)
    [junit]         at com.google.inject.internal.InjectorImpl.createJustInTimeBindingRecursive(InjectorImpl.java:568)
    [junit]         at com.google.inject.internal.InjectorImpl.getJustInTimeBinding(InjectorImpl.java:167)
    [junit]         at com.google.inject.internal.InjectorImpl.getBindingOrThrow(InjectorImpl.java:127)
    [junit]         at com.google.inject.internal.InjectorImpl.getInternalFactory(InjectorImpl.java:642)
    [junit]         at com.google.inject.internal.FactoryProxy.notify(FactoryProxy.java:43)
    [junit]         at com.google.inject.internal.BindingProcessor.runCreationListeners(BindingProcessor.java:238)
    [junit]         at com.google.inject.internal.InjectorBuilder.initializeStatically(InjectorBuilder.java:134)
    [junit]         at com.google.inject.internal.InjectorBuilder.build(InjectorBuilder.java:108)
    [junit]         at com.google.inject.Guice.createInjector(Guice.java:93)
    [junit]         at com.google.inject.Guice.createInjector(Guice.java:70)
    [junit]         at com.google.inject.Guice.createInjector(Guice.java:60)
    [junit]         at com.googlecode.guice.bundle.OSGiTestActivator.start(OSGiTestActivator.java:489)
    [junit]         at org.apache.felix.framework.util.SecureAction.startActivator(SecureAction.java:661)
    [junit]         at org.apache.felix.framework.Felix.activateBundle(Felix.java:1760)
    [junit]         ... 21 more
    [junit] Caused by: com.google.inject.internal.ComputationException: com.google.inject.internal.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null
    [junit]         at com.google.inject.internal.MapMaker$StrategyImpl.compute(MapMaker.java:553)
    [junit]         at com.google.inject.internal.MapMaker$StrategyImpl.compute(MapMaker.java:419)
    [junit]         at com.google.inject.internal.CustomConcurrentHashMap$ComputingImpl.get(CustomConcurrentHashMap.java:2041)
    [junit]         at com.google.inject.internal.FailableCache.get(FailableCache.java:46)
    [junit]         at com.google.inject.internal.MembersInjectorStore.get(MembersInjectorStore.java:63)
    [junit]   ...

_Original issue: http://code.google.com/p/google-guice/issues/detail?id=517_