Omnibus patch for 4.7 compatibility

Building on other patches, and making use of syntax from admin pages which were not broken before, I offer this quite-large patch against current CVS to bring Trackback up to 4.7.

It does the following:

• Adds a 'select all' widget to admin table lists
• Fixes admin/trackback/approval, which now lists more than one item and allows actions to be performed correctly
• Fixes admin/trackback, which was also showing only one trackback in its list view until now

It does not yet fix the following bug:

• Choosing 'mark as spam' on a checked list does not work (for me) at this point, appearing instead to operate only on the first trackback ID presented in the array.

Still... if you're *not* using Jeremy's current spam.module (which is hosted off-site), this patch brings the module into full compliance.