Wrong check for case insensitive duplicate archive entries

[Bananeweizen]

I see this lots of these warnings in a Tycho build:

[WARNING] Archive entry 'org/eclipse/tycho/plugins/p2/extras/Repository.java' and existing file 'C:\dev\tycho\git\tycho\tycho-extras\tycho-eclipserun-plugin\target\maven-plugin-plugin-sources\org.eclipse.tycho.extras\tycho-p2-extras-plugin\4.0.0-SNAPSHOT\sources\org\eclipse\tycho\plugins\p2\extras\Repository.java' names differ only by case. This may lead to an unexpected outcome on case-insensitive filesystems.
[WARNING] Archive entry 'META-INF/m2e/lifecycle-mapping-metadata.xml' and existing file 'C:\dev\tycho\git\tycho\tycho-extras\tycho-eclipserun-plugin\target\maven-plugin-plugin-sources\org.eclipse.tycho.extras\tycho-p2-extras-plugin\4.0.0-SNAPSHOT\sources\META-INF\m2e\lifecycle-mapping-metadata.xml' names differ only by case. This may lead to an unexpected outcome on case-insensitive filesystems.
[WARNING] Archive entry 'META-INF/maven/org.eclipse.tycho.extras/tycho-p2-extras-plugin/pom.xml' and existing file 'C:\dev\tycho\git\tycho\tycho-extras\tycho-eclipserun-plugin\target\maven-plugin-plugin-sources\org.eclipse.tycho.extras\tycho-p2-extras-plugin\4.0.0-SNAPSHOT\sources\META-INF\maven\org.eclipse.tycho.extras\tycho-p2-extras-plugin\pom.xml' names differ only by case. This may lead to an unexpected outcome on case-insensitive filesystems.

That's raised by a check for archive entry names that are identical except for different case. However, these are all false positives since the warning is raised because of the 2 compared Strings differing in their file separator, e.g. the relevant parts from the first message are:

org\eclipse\tycho\plugins\p2\extras\Repository.java
org/eclipse/tycho/plugins/p2/extras/Repository.java

This has also been discussed in #180, but I feel that change is not sufficient, since both inputs need to be normalized.