Fix for issue #847
Fix for issue #847

The GUFuncBuilder needs to remember the order in which signatures
were specified in order to select the correct implementation for
function dispatch. This commit implements this based on similar
functionality in UFuncBuilder.

IntelLabs/numba,pitrou/numba,jriehl/numba,jriehl/numba,gmarkall/numba,ssarangi/numba,jriehl/numba,gdementen/numba,sklam/numba,IntelLabs/numba,seibert/numba,seibert/numba,numba/numba,stonebig/numba,gmarkall/numba,sklam/numba,numba/numba,numba/numba,cpcloud/numba,seibert/numba,cpcloud/numba,pombredanne/numba,IntelLabs/numba,ssarangi/numba,gdementen/numba,stuartarchibald/numba,gdementen/numba,stuartarchibald/numba,pitrou/numba,IntelLabs/numba,sklam/numba,cpcloud/numba,stuartarchibald/numba,stuartarchibald/numba,GaZ3ll3/numba,pitrou/numba,jriehl/numba,GaZ3ll3/numba,pitrou/numba,IntelLabs/numba,stuartarchibald/numba,stonebig/numba,pombredanne/numba,pombredanne/numba,sklam/numba,ssarangi/numba,GaZ3ll3/numba,ssarangi/numba,seibert/numba,pombredanne/numba,seibert/numba,stefanseefeld/numba,pombredanne/numba,pitrou/numba,stefanseefeld/numba,GaZ3ll3/numba,numba/numba,stefanseefeld/numba,gmarkall/numba,jriehl/numba,stonebig/numba,GaZ3ll3/numba,cpcloud/numba,gdementen/numba,stonebig/numba,gmarkall/numba,numba/numba,stefanseefeld/numba,gmarkall/numba,stefanseefeld/numba,gdementen/numba,sklam/numba,ssarangi/numba,cpcloud/numba,stonebig/numba