[1.2.X] Fixed #15024 -- Ensure that choice of L10N format module used is...

[1.2.X] Fixed #15024 -- Ensure that choice of L10N format module used is stable given a stable setup of format modules in ll/ and ll_CC/ dirs. Thanks David Reynolds for the report and suggestions leading to the solution.

Backport of [15183] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15184 bcc190cf-cafb-0310-a4f2-bffc1f526a37