[1.2.X] Fixed #11434 -- Corrected style of arrow buttons located at the center...

[1.2.X] Fixed #11434 -- Corrected style of arrow buttons located at the center of filter_{horizontal|vertical} m2m widgets to not give them focus borders that span from the left page border. Thanks defaultwombat for the report and patch.

Backport of [15144] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15181 bcc190cf-cafb-0310-a4f2-bffc1f526a37