pip bundle pkg fails if pkg tarball contains .hg dir and mercurial not installed

[mwhudson]

Currently, the tarball for python-keyring contains .hg files (guess they didn't use sdist) and if hg is not installed, pip bundle keyring fails:

$ pip bundle lava.pybundle keyring
Putting temporary build files in /srv/lava/instances/dev/build-bundle5 and source/develop files in /srv/lava/instances/dev/src-bundle
Downloading/unpacking keyring
  Downloading keyring-0.7.1.zip (40Kb): 40Kb downloaded
  Running setup.py egg_info for package keyring

  Running setup.py egg_info for package keyring

Cannot find command 'hg'
Storing complete log in /home/mwhudson/.pip/pip.log

The workaround is clear (install hg) but this is unexpected.