[1.2.X] Fixed #17846 -- Made a note about the micro-version in which a security fix for URLField was introduced in the 1.2.X branch more accurate.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@17677 bcc190cf-cafb-0310-a4f2-bffc1f526a37