[issue] blank dive->location values update from a newly set location value

[Lubomir I. Ivanov]

a small bug / issue:

i've recorded an animated gif. you can check it in your browser (700kb):
http://dl.dropbox.com/u/1627980/subsurface/subsurface_bug0.gif

lets say, if the dive->location values for a set of dives are blank and one of
these is then set to some new value (that populates the combobox list -
GtkListStore), selecting one of the blank-location dives and moving away from
it, sets its value to the same value of the only dive (the last edited one) that
has its location populated - if that makes any sense.

same applies to "divemaster" and "buddy", but not for "notes" i believe.
i cannot pinpoint the exact cause yet, but it might be related to the fact that
"location_changed" (and *_changed in info.c) are globals always set to 1?

lubomir