egg-post-commit should only automatically upload an egg if (1) it
detects a change in the directory for the egg's latest release and (2)
the egg's directory doesn't have the 'autoupdate' Subversion property
set to 'no'.
The directory for an egg's latest release would be:
1. If the egg has a 'tags' directory,
1.1. If the 'tags' directory has a 'latest' property set to 'foo',
the directory is 'tags/foo'.
1.2. Otherwise, the directory under 'tags' corresponding to the
greatest version number.
2. The egg's directory.