Merge branch 'tree2' of git://git.hohndel.org/subsurface

Merge branch 'tree2' of git://git.hohndel.org/subsurface

Pull selection tracking fixes from Dirk Hohndel:
 "I just gave up on gtk tracking our selection.  Way too much pain.  The
  implementation below has seen some testing with the debugging code
  enabled and seems to work - but it needs more banging onto it, I'm
  sure.

  Ideally I'd like to leave the debug code in, ask people on the mailing
  list to play with it and report any inconsistencies.  After that I'll
  be happy to remove it again."

* 'tree2' of git://git.hohndel.org/subsurface:
  Stop relying on gtk to track which dives are selected