Add LockException to locks for completeness

[magneto]

in django/core/files/locks.py

All is well, except for the Specific Exception "Resource Unavailable" (IO Error #11) which usually means the file is already locked.

Rather then doing an

except IOError, err:
     if err[0] == 11:
         "Do something with Already Locked"
    else:
        raise

on can simply have a LockException in locks

Not sure if this was a design thought at the beginning, or just a little omission.

This follows from the version on ​http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/65203

I'm not sure how to do this on windows, perhaps someone else knows?

[magneto]

Lock Exception

[(none)]

Milestone post-1.0 deleted

[Jacob]

django.core.files.locks only exists for internal use, which means unless something else in django.core.files needs a change like this, we don't need to make it. Since this isn't needed by the core, there's no reason to make this change.