Bug 1293234 - Use octal notation for permission modes in the build system; r=gps

As of Python 3, decimal notations of octal values for permission modes
are no longer permitted and will result in a `SyntaxError` exception
(`invalid token`).

Using the proper octal notation which is also Python 2.7 compatible will
fix this issue.

configure.py

@@ -81,7 +81,7 @@ if __name__ == '__main__':
 
     # Other things than us are going to run this file, so we need to give it
     # executable permissions.
-    os.chmod('config.status', 0755)
+    os.chmod('config.status', 0o755)
     if config.get('MOZ_BUILD_APP') != 'js' or config.get('JS_STANDALONE'):
         os.environ['WRITE_MOZINFO'] = '1'
         # Until we have access to the virtualenv from this script, execute