Test and possible workaround for https://github.com/astropy/astropy/issues/2749
Handle a misconfigured LC_CTYPE in a few more places, including when importing Sphinx (since that can lead down a rabbit hole that results in calling locale.getdefaultlocale() which in turn invokes http://bugs.python.org/issue18378--in this case a useful warning is displayed and Sphinx is just considered not importable.
Added changelog entry
Merge pull request #58 from embray/issue-2749

Test and possible workaround for Astropy #2749