Fixes to wcs/test_extension.py
Fixes to wcs/test_extension.py

If compilation of the test extension fails, mark the test as skipped,
since it probably just indicates the user doesn't have a working
compilation environment.

Don't ever skip on Travis, since a failure there indicates something
more serious.

DougBurke/astropy,MSeifert04/astropy,lpsinger/astropy,bsipocz/astropy,AustereCuriosity/astropy,stargaser/astropy,larrybradley/astropy,tbabej/astropy,MSeifert04/astropy,mhvk/astropy,saimn/astropy,AustereCuriosity/astropy,pllim/astropy,pllim/astropy,dhomeier/astropy,bsipocz/astropy,stargaser/astropy,tbabej/astropy,funbaker/astropy,funbaker/astropy,dhomeier/astropy,StuartLittlefair/astropy,lpsinger/astropy,larrybradley/astropy,kelle/astropy,astropy/astropy,aleksandr-bakanov/astropy,saimn/astropy,joergdietrich/astropy,joergdietrich/astropy,AustereCuriosity/astropy,MSeifert04/astropy,StuartLittlefair/astropy,stargaser/astropy,aleksandr-bakanov/astropy,AustereCuriosity/astropy,DougBurke/astropy,tbabej/astropy,mhvk/astropy,tbabej/astropy,joergdietrich/astropy,StuartLittlefair/astropy,kelle/astropy,dhomeier/astropy,funbaker/astropy,kelle/astropy,saimn/astropy,lpsinger/astropy,mhvk/astropy,astropy/astropy,funbaker/astropy,kelle/astropy,bsipocz/astropy,pllim/astropy,pllim/astropy,astropy/astropy,StuartLittlefair/astropy,mhvk/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,astropy/astropy,pllim/astropy,joergdietrich/astropy,stargaser/astropy,tbabej/astropy,bsipocz/astropy,AustereCuriosity/astropy,dhomeier/astropy,joergdietrich/astropy,astropy/astropy,DougBurke/astropy,larrybradley/astropy,larrybradley/astropy,saimn/astropy,MSeifert04/astropy,lpsinger/astropy,StuartLittlefair/astropy,mhvk/astropy,DougBurke/astropy,aleksandr-bakanov/astropy,kelle/astropy,larrybradley/astropy,saimn/astropy,dhomeier/astropy