Speed up matVecModM function.
Merge pull request #1759 from MarcCote/speedup_MRG_init

Speed up matVecModM function.
CRASH: Make sure we don't bust the threads.z 64 limites.
Make sure dtype is int64 as before and comment code that isn't used.
More info in error message.
Don't print waiting for the lock the first time.
CRASH FIX: same fix crash to the new gpu back-end
remove import not used.
Merge pull request #1761 from nouiz/mixed

Mixed