fixed minor multiprocessing issue

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@1103 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/Utils/threading.py

@@ -204,6 +204,7 @@ def init_threading(number_of_processes=None, enable_server=False, remote=None,
             # no further warnings required
             pass
     else:
+        import multiprocessing
         if number_of_processes is None:
             # use defaults
             # don't enable threading for a single cpu