Add a jitted version of set_num_threads for testing purposes
Add a jitted version of set_num_threads for testing purposes

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