[MDEP-458] overwriteIfNewer forces not needed overwrite of already existing artifacts

**[Reguel Wermelinger](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=lordeagle)** opened **[MDEP-458](https://issues.apache.org/jira/browse/MDEP-458?redirect=false)** and commented

The __ property does not work for classifier _sources_ . As soon as the overWriteIfNever property is enabled, the artifacts with classifier "sources" are always overwritten. So not needed files are written very often to the disk.

The flag seems to work as expected for executions where no classifier is specified.

See the attached sample project where execution "thirdparty" can handle overwriteIfNever correctly. While the execution "thirdparty.sources" always copies files to the disk:

```xml
[INFO] --- maven-dependency-plugin:2.9-SNAPSHOT:copy-dependencies (thirdparty) @ ch.ivyteam.testarea.overwrite ---
[INFO] junit:junit:jar:3.8.1 already exists in destination.
[INFO]
[INFO] --- maven-dependency-plugin:2.9-SNAPSHOT:copy-dependencies (thirdparty.sources) @ ch.ivyteam.testarea.overwrite ---
[INFO] Copying junit-3.8.1-sources.jar to D:\dev\trunk\real_workspaceKepler\ch.ivyteam.testarea.overwrite\lib\mvn-src\junit-3.8.1-sources.jar
```

The not yet released version 2.9 in use was: maven-dependency-plugin-2.9-20140907.174645-631

---

**Affects:** 2.8, 2.9

**Attachments:**
- [overwriteIfNewer-sample.zip](https://issues.apache.org/jira/secure/attachment/12715121/overwriteIfNewer-sample.zip) (_270.36 kB_)

Start with the attached overwriteIfNewer-sample.zip and compare the copy-dependencies executions "thirdparty" and "thirdparty.sources", focusing on how the sources classifier is handled. Verify the fix against the reported logs: with overwriteIfNever enabled, an existing sources artifact should not be copied again, while the no-classifier execution must retain its current behavior.

Written by the indexing model from the issue text.