Improve JavaScript "check all" functionality on forms

The "check all" aka "select all" checkboxes should reflect the current
state of the checkboxes they're linked to. If a user clicks on "Select
All" on view_all_bug_page and then proceeds to uncheck some of the
issues one by one, the "Select All" checkbox should no longer be
checked.

It should be noted that jQuery doesn't correctly handle
addition/modification/removal of attributes for documents served as
Content-Type: application/xhtml+xml. jQuery bug 0004283 provides further
information at http://bugs.jquery.com/ticket/4283.