This patch basically bypasses setup.py for pure Python packages. Instead
of producing .egg-info directories in the source tree, it merely
installs .pth files pointing back to the source directory. As a result,
this is less junk in the source tree.
The .hgignore and .gitignore entries for egg-info directories have been
removed because there should no longer be egg-info directories any more.
People should clean up these orphaned directories manually. This can be
accomplished by running:
$ hg status -u | grep .egg-info | xargs rm -rf
$ git ls-files -o '*.egg-info*' | xargs rm -rf
