Issue2535

This is probably an improvement, but definitely an annoyance.

Tom, as preparation to work on #527524 I recently looked into the part of Jython responsible to generate class-files. However I suppose I could fix this one too. The question is, how should the files in the stacktrace be named?
- The JVM usually prints filenames without path, e.g. plainly 'PyObject.java'.
- CPython usually prints full, absolute path, e.g. '/usr/lib/python2.7/platform.py'.
So in a sense Java and Python conventions clash here.
Maybe the best compromise is to store paths relatively to Jython's build-directory (i.e. dist) and display them somehow like '<jython-home>/Lib/platform.py'.
Files not in a Jython-subfolder can continue to use CPython-style, since they are likely just compiled locally.
Also, we should have a flag or something in compileall.py to specify a format, e.g. a base-path relatively from which filenames should be stored in generated classfiles.

Fixed as of https://github.com/jythontools/jython/commit/2ce0a4e51c6c020f11adcd0e59bfb901e4fea8ba
See commit-message for choosen format.
Tom, does this fix stacktraces properly for you?