Add catch for unknown threading layer requested
Add catch for unknown threading layer requested

gmarkall/numba,stuartarchibald/numba,gmarkall/numba,seibert/numba,numba/numba,jriehl/numba,seibert/numba,stonebig/numba,numba/numba,cpcloud/numba,IntelLabs/numba,stonebig/numba,gmarkall/numba,sklam/numba,stuartarchibald/numba,cpcloud/numba,cpcloud/numba,jriehl/numba,seibert/numba,cpcloud/numba,seibert/numba,jriehl/numba,IntelLabs/numba,IntelLabs/numba,sklam/numba,gmarkall/numba,stonebig/numba,IntelLabs/numba,stuartarchibald/numba,IntelLabs/numba,seibert/numba,stuartarchibald/numba,numba/numba,cpcloud/numba,stuartarchibald/numba,numba/numba,gmarkall/numba,jriehl/numba,sklam/numba,stonebig/numba,sklam/numba,sklam/numba,stonebig/numba,numba/numba,jriehl/numba