Fix race condition during `mimetypes` initialization.
Fix race condition during `mimetypes` initialization.

Initial patch from Steven R. Loomis.
Closes #8629.


git-svn-id: 0d96b0c1a6983ccc08b3732614f4d6bfcf9cbb42@9740 af82e41b-90c4-0310-8c96-b1721e28e2e2

rbaumg/trac,rbaumg/trac,rbaumg/trac,rbaumg/trac