Refs #294. Used pthread_atfork to avoid hang after a Unix fork.

The problem is the mutex we used in blas_server. Thus, we must clear
the mutex before the fork and re-init them at parent and child process.

If you used OpenMP, GOMP has the same problem by now. Please try other OpenMP
implemantation.

driver/others/blas_server_omp.c

@@ -315,4 +315,9 @@ int exec_blas(BLASLONG num, blas_queue_t *queue){
   return 0;
 }
 
+void openblas_fork_handler()
+{
+
+}
+
 #endif