allow underscores in arch names
allow underscores in arch names

Stops it barfing on arch(x86_64).

edsko/cabal,fugyk/cabal,sopvop/cabal,thomie/cabal,typelead/epm,anton-dessiatov/cabal,ian-ross/cabal,eric-stanley/cabal,enolan/cabal,rimmington/cabal,thoughtpolice/cabal,plumlife/cabal,alphaHeavy/cabal,thomie/cabal,garetxe/cabal,Heather/cabal,ian-ross/cabal,Helkafen/cabal,lukexi/cabal,martinvlk/cabal,headprogrammingczar/cabal,sopvop/cabal,seereason/cabal,kolmodin/cabal,typelead/epm,seereason/cabal,rimmington/cabal,corngood/cabal,kolmodin/cabal,kosmikus/cabal,kosmikus/cabal,mightybyte/cabal,fpco/cabal,thoughtpolice/cabal,garetxe/cabal,randen/cabal,themoritz/cabal,plumlife/cabal,x-y-z/cabal,Peaker/cabal,corngood/cabal,randen/cabal,Helkafen/cabal,triplepointfive/cabal,beni55/cabal,ghc-android/cabal,bennofs/cabal,gridaphobe/cabal,valderman/cabal,bennofs/cabal,headprogrammingczar/cabal,edsko/cabal,Peaker/cabal,mydaum/cabal,valderman/cabal,x-y-z/cabal,themoritz/cabal,mmakowski/cabal,gbaz/cabal,eric-stanley/cabal,mydaum/cabal,Heather/cabal,plow-technologies/cabal,sopvop/cabal,trskop/cabal,gridaphobe/cabal,martinvlk/cabal,mightybyte/cabal,ghc-android/cabal,christiaanb/cabal,christiaanb/cabal,gbaz/cabal,lukexi/cabal,anton-dessiatov/cabal,enolan/cabal,plow-technologies/cabal,mmakowski/cabal,fpco/cabal,trskop/cabal,themoritz/cabal,fugyk/cabal,alphaHeavy/cabal,beni55/cabal,triplepointfive/cabal