Dive edit: do a better job noticing when the coordinates were changed

Previously the code could get confused by edits (including trivial things
like deleting the coordinates). It seems much more reliable to simply
compare the coordinates of the edited dive with the ones in the current
dive before the edits.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix incorrect argument order for %.*f

Strangely, *prinf() on Linux appears to do the right thing in either
order (my guess is based on the type of the two values?), but on Windows
things go badly.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>