Fixed a bug that caused rc parameters to not be reset to initial state if an exception happened while setting new rc parameters inside rc_context.
Minor fixes
raise SkipTest if not using Python >= 2.7
Merge pull request #3752 from astrofrog/rc_context_exceptions

BUG : Make sure that initial state gets reset if anything goes wrong in ``rc_context``
Final decxx corrections to PR 3723
Merge pull request #3744 from ianthomas23/final_decxx_corrections

Final decxx corrections to PR #3723