Fixes and test clean-up related to return values.

Fixes:
- Returned custom object string representations and dict keys support Unicode.

Test clean-up:
- Added separate lib for return values. Old atestlibrary.py wasn't needed anymore after that. Yay!
- Cleaned up and enhanced return value tests in general.
Test fixes/cleanup: Support Windows paths. Made path variable.
Test cleanup: Safer server stopping.

Stop Remote Server keyword is guaranteed to stop the server. Terminating
the process wasn't enough on Windows with jython.bat -- just the batch
process was terminated but java.exe with the server left running.
Copyright update + enhanced TODO comment
Test cleanup: Enhanced argument type tests a bit and cleaned them up by taking new possibility to use Evaluate with a custom namespace into use.