Added option to add Java properties to the Jython interpreter invocation.

This is especially useful if you want to set the Jython cache file to a folder
that your process controlls.  E.g.:

  $ gsh.jython -p "python.cachedir=$CACHEDIR" myscript.py
Merge pull request #9 from cwaldbieser/multi_shell

Added option to add Java properties to the Jython interpreter invocation...