Complete a merge of the mimelib project and the Python cvs codebases

Complete a merge of the mimelib project and the Python cvs codebases
for the email package.  The former is now just a shell project that
has some extra files for packaging for independent use (e.g. setup.py
and README).

Added a compatibility layer so that the same API can be used in Python
2.1 and 2.2/2.3 with the major differences shuffled off into helper
modules (_compat21.py and _compat22.py).

Also bumped the package version number to 2.0.3 for some fixes to be
checked in momentarily.