Fix a typo that was breaking the open files test
Merge pull request #780 from mdboom/setup/pkg-config-pkg-missing

Add default libraries to the list if the pkg-config lookup fails
This should fix #779. As @mdboom explained these equivalencies should be using the value of c (in m/s) as a scaling factor, but its units shouldn't really come into it. This should have been changed to c.value and h.value as part of #745.
fix another typo related to subprocesses in open file detection
Merge pull request #782 from eteq/fix-failing-open-file-test

Fix failing open file test
Merge pull request #779 from iguananaut/issue-779

Quantity throws an unrelated warning when converting through equivalencies?
Extract messages from wcslib about rejected (non-standard) keywords and convert them into Python warnings.
Upgrade to wcslib-4.17
Progress
Add documentation for wcslint
Fix for Python 2.6, which is missing PyErr_NewExceptionWithDoc