Add sourcePath or sourceFile to xdoc report

[kloessst]

The xdoc report currently only uses the class name to locate the bug instance. While it is possible to re-construct the source file in most cases, classes with inner classes are troublesome as the '$' delimiter could also be part of the name of the outer class.

Does something speak against adding a sourceFile or sourcePath attribute to the file element? Had a quick look at the code and especially sourceFile should be easy to add.