[1.2.X] Fixed #11966 -- Made it possible to use a percent sign in a...

[1.2.X] Fixed #11966 -- Made it possible to use a percent sign in a translation message id. Thanks for the patch, Claude Paroz.

Backport from trunk (r14459).

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14460 bcc190cf-cafb-0310-a4f2-bffc1f526a37