Travis: allow user forks
Travis: allow user forks

Check for each submodule repository url if the user made its own fork.
If so, use that. Otherwise, fall back on the one from github.com/ghc.

As suggested by Richard in this mailinglist discussion:
https://mail.haskell.org/pipermail/ghc-devs/2014-November/007300.html

Documentation is at [wiki:TestingPatches#Travis].

Differential Revision: https://phabricator.haskell.org/D939

nkaretnikov/ghc,tjakway/ghcjvm,ezyang/ghc,oldmanmike/ghc,gridaphobe/ghc,AlexanderPankiv/ghc,acowley/ghc,mcschroeder/ghc,mcschroeder/ghc,anton-dessiatov/ghc,vTurbine/ghc,sdiehl/ghc,mettekou/ghc,gridaphobe/ghc,AlexanderPankiv/ghc,vikraman/ghc,ml9951/ghc,snoyberg/ghc,tjakway/ghcjvm,anton-dessiatov/ghc,oldmanmike/ghc,acowley/ghc,GaloisInc/halvm-ghc,ezyang/ghc,ezyang/ghc,mettekou/ghc,urbanslug/ghc,ghc-android/ghc,siddhanathan/ghc,ghc-android/ghc,da-x/ghc,tjakway/ghcjvm,urbanslug/ghc,GaloisInc/halvm-ghc,shlevy/ghc,tjakway/ghcjvm,wxwxwwxxx/ghc,sgillespie/ghc,tjakway/ghcjvm,mettekou/ghc,vikraman/ghc,ml9951/ghc,ezyang/ghc,snoyberg/ghc,mfine/ghc,nkaretnikov/ghc,olsner/ghc,elieux/ghc,shlevy/ghc,vikraman/ghc,da-x/ghc,GaloisInc/halvm-ghc,AlexanderPankiv/ghc,wxwxwwxxx/ghc,olsner/ghc,anton-dessiatov/ghc,mfine/ghc,mettekou/ghc,acowley/ghc,oldmanmike/ghc,wxwxwwxxx/ghc,sdiehl/ghc,ghc-android/ghc,acowley/ghc,ezyang/ghc,tjakway/ghcjvm,vikraman/ghc,da-x/ghc,vTurbine/ghc,elieux/ghc,ml9951/ghc,ezyang/ghc,acowley/ghc,ezyang/ghc,mcschroeder/ghc,nkaretnikov/ghc,acowley/ghc,siddhanathan/ghc,elieux/ghc,anton-dessiatov/ghc,gridaphobe/ghc,siddhanathan/ghc,sdiehl/ghc,vTurbine/ghc,mettekou/ghc,mettekou/ghc,sgillespie/ghc,snoyberg/ghc,ml9951/ghc,shlevy/ghc,elieux/ghc,sdiehl/ghc,TomMD/ghc,mcschroeder/ghc,mcschroeder/ghc,ghc-android/ghc,TomMD/ghc,ghc-android/ghc,vikraman/ghc,nushio3/ghc,nushio3/ghc,nushio3/ghc,vikraman/ghc,sdiehl/ghc,sgillespie/ghc,AlexanderPankiv/ghc,AlexanderPankiv/ghc,nkaretnikov/ghc,snoyberg/ghc,shlevy/ghc,mfine/ghc,shlevy/ghc,urbanslug/ghc,GaloisInc/halvm-ghc,snoyberg/ghc,olsner/ghc,da-x/ghc,oldmanmike/ghc,nushio3/ghc,ml9951/ghc,sdiehl/ghc,wxwxwwxxx/ghc,wxwxwwxxx/ghc,urbanslug/ghc,vikraman/ghc,sgillespie/ghc,ghc-android/ghc,nushio3/ghc,ml9951/ghc,anton-dessiatov/ghc,da-x/ghc,mfine/ghc,olsner/ghc,da-x/ghc,snoyberg/ghc,sgillespie/ghc,mcschroeder/ghc,siddhanathan/ghc,sdiehl/ghc,ml9951/ghc,wxwxwwxxx/ghc,TomMD/ghc,da-x/ghc,AlexanderPankiv/ghc,anton-dessiatov/ghc,shlevy/ghc,vTurbine/ghc,tjakway/ghcjvm,vTurbine/ghc,mfine/ghc,vTurbine/ghc,gridaphobe/ghc,mcschroeder/ghc,TomMD/ghc,GaloisInc/halvm-ghc,elieux/ghc,siddhanathan/ghc,gridaphobe/ghc,GaloisInc/halvm-ghc,urbanslug/ghc,nkaretnikov/ghc,sgillespie/ghc,AlexanderPankiv/ghc,ghc-android/ghc,elieux/ghc,acowley/ghc,TomMD/ghc,mfine/ghc,olsner/ghc,oldmanmike/ghc,gridaphobe/ghc,TomMD/ghc,siddhanathan/ghc,elieux/ghc,vTurbine/ghc,sgillespie/ghc,mfine/ghc,oldmanmike/ghc,ml9951/ghc,siddhanathan/ghc,nushio3/ghc,urbanslug/ghc,urbanslug/ghc,olsner/ghc,oldmanmike/ghc,nkaretnikov/ghc,nushio3/ghc,wxwxwwxxx/ghc,snoyberg/ghc,GaloisInc/halvm-ghc,olsner/ghc,mettekou/ghc,TomMD/ghc,anton-dessiatov/ghc,gridaphobe/ghc,nkaretnikov/ghc,shlevy/ghc