Fix problems building on windows.
Fix problems building on windows.

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