merged defaultfile and the other outstanding fixes

[Dirk Hohndel]

Getting closer. This should include all outstanding fixes that I found.

Please test. I want to make sure that the file handling logic is
robust. Random sequences of opening, closing, saving, importing,
quitting, deleting dives, adding dives, changing trips... it all needs
to stay consistent.

Also any other corner cases that you can think of - now is the time to
find the bugs.

My current plan is to wait for at least one, maybe two (depending on how
things work out) weeks of testing and bug fixing. This should also give
Jacco a chance to catch up with the documentation and for the packagers
to figure out the details (as I would ideally like to have the auxiliary
files for packaging in the git tree).

It would be great to make sure we have solid Windows and Mac binaries -
which brings me to the odd gtk/glib/ptreads bug. I cannot figure out how
to make progress on this. Valgrind shows nothing obvious, setting
various breakpoints and peeking at the data structures hasn't been much
help, either. Lubomir's attempts to fix the crashes appear to have gone
nowhere as far as I can tell.

Miika, can you still reproduce this on Ubuntu? I don't have my Ubuntu
machine with me on this trip, so I can't test this until I'm back home.

Any help to squash this one would be extremely welcome...

Please let me know if there's anything else that we should consider for
2.0.

/D