1.0.3dev: Improved layout of elements on the //Advanced// prefs panel.

Added `userprefs` `id` to the form, for consistency with other prefs panels.


git-svn-id: http://trac.edgewall.org/intertrac/log:/branches/1.0-stable@13262 af82e41b-90c4-0310-8c96-b1721e28e2e2