Fix applysizehints: Account for SHAPE borders
Mark stuff that's probably "broken" since SHAPE borders

I haven't seen any major bugs regarding this stuff. However, it's most
likely not correct code. Haven't checked yet.
Fix handling of SHAPE borders in manage()

Does 6811653 the right way and changes upstream behaviour.
Simplify hiding of clients

As we're using "* -2" here, the exact border sizes don't matter at all.
Fix applysizehints (interactive): Account for SHAPE borders