Added support for pandas installed directly from git trunk

pandas.version == commit_hash when pandas is installed from git trunk
Use pandas.version.short_version
MAINT: Change back to path for build box
Merge pull request #1315 from jseabold/fix-updateweb-buildbox

MAINT: Change back to path for build box
Merge pull request #1185 from invisibleroads/patch-1

BLD: Add support for installing when pandas is a shallow clone.