Patch largely based on changes by Andrew Dalke, as discussed in the
distutils-sig.

yours, please let me know for propoer acknowledgement.)

This avoids recompiling files that haven't changed; it adds a -f
option to force recompilation.

- added docstrings
- support option to specify a different purported directory name
- reindented with 4 spaces

urllib.py: '+' is not always safe (even though the RFC says so :-( )
whrandom.py: throw away top bits of time to avoid overflow on Mac
(where times can be negative)