Don't waste time scanning the 'mayan/media' directory

Is not relevant for packaging and can cause slow execution
if ran from an existing installation

setup.py

@@ -42,6 +42,7 @@ def find_packages(directory):
         os.chdir(root_dir)
 
     for dirpath, dirnames, filenames in os.walk(directory):
+        if not dirpath.startswith('mayan/media'):
             # Ignore dirnames that start with '.'
             if os.path.basename(dirpath).startswith('.'):
                 continue