planner and dive add should work now

[Dirk Hohndel]

I ran Subsurface under Valgrind and that quickly pointed out a few more
issues. With the latest changes I pushed I believe add dive and the
planner are now functional and random combinations of them no longer crash
Subsurface or confuse the dive list.

I would really appreciate if people could try HARD to break this... there
were some rather subtle yet nasty bugs in the code.

Thanks

/D