Merge pull request #68 from jmchilton/master

Do not attempt to install condor on 12.04 LTS.
Provide a more flexible way to determine pip executable. Thanks to Tim Fennell
Check for TMPDIR on systems where missing environmental varialbles cause errors. Thanks to Tim Fennell
Avoid using pwd which fails on some shells. Inject current system install into path when checking for programs for installation into non-system paths
Flexibly choose between default python and python with extension based on version numbers. Thanks to Tim Fennell
Idea for create virtualenvs for multiversioned Galaxy tools.