On my Mac, /usr/local/bin/python2.5 is a symlink to
"../../../Library/Frameworks/Python.framework/Versions/2.5/bin/python2.5".

When I install Mercurial from source, the "mercurial" package is
installed at "/usr/local/lib/python2.5/site-packages/mercurial", so the
installation is broken.  Since "site-packages" appears nowhere in the
Mercurial source tree, I think it's setuptools (not Mercurial) that is
getting this wrong.

Mercurial's setup.py can be seen here:

(as of this writing)
http://hg.intevation.org/mercurial/crew/file/628da4a91628/setup.py

(the latest)
http://hg.intevation.org/mercurial/crew/file/tip/setup.py

I'm not sure what the Right Thing would be, but if it's agreed that the
current behavior is a hack, then `(p for p in sys.path if
p.endswith('site-packages')).next()`, falling back to the current
behavior, seems like a better hack.

Happy to patch, if someone can advise me; MvL?