do race-able check before making directory, to reduce # of directory creation attempts

theano/gof/lazylinker_c.py

@@ -30,6 +30,7 @@ try:
     # compile_str()) but if another lazylinker_ext does exist then it will be
     # imported and compile_str won't get called at all.
     location = os.path.join(config.compiledir, 'lazylinker_ext')
+    if not os.path.exists(location):
         try:
             # Try to make the location
             os.mkdir(location)
@@ -42,8 +43,6 @@ try:
             assert 'Errno 17' in str(e)
             assert os.path.isdir(location)
 
-    if not os.path.exists(location):
-        os.mkdir(location)
     if not os.path.exists(os.path.join(location, '__init__.py')):
         file(os.path.join(location, '__init__.py'), 'w').close()