In Python 2.6.2, the fix for the issue 5401 changed the way the
mimetypes module is initialized.

But now the initialization is not thread-safe : a thread can set
``inited`` to ``True`` and then be preempted before to overwrite the
functions guess_type(), guess_extension() ...

With such a partial initialization, the next thread will raise an 
excessive recursion exception when calling one of this functions.

A fix could be to wrap ``mimetypes.init()`` with a thread lock.