Fixed #10061 -- Added namespacing for named URLs - most importantly, for the admin site, where the absence of this facility was causing problems. Thanks to the many people who contributed to and helped review this patch.

This change is backwards incompatible for anyone that is using the named URLs
introduced in [9739]. Any usage of the old admin_XXX names need to be modified
to use the new namespaced format; in many cases this will be as simple as a
search & replace for "admin_" -> "admin:". See the docs for more details on
the new URL names, and the namespace resolution strategy.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11250 bcc190cf-cafb-0310-a4f2-bffc1f526a37