Adds Ubuntu/numpy 1.4.x segfault warning to known issues
Adds Ubuntu/numpy 1.4.x segfault warning to known issues

Closes #791

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