Fix some problems with get_version() in setup.py
Fix some problems with get_version() in setup.py

When called from distutils.core.run_setup():
- get_version() may not rely on globals
- there is no sys.argv[1]

When check-manifest creates an sdist, there is no git context nor a
PKG-INFO file.

brechtm/rinohtype,brechtm/rinohtype,brechtm/rinohtype