which is just a #define to g_assert for now, but can now easily be
turned into something that does some nicer debugging using our new
stack trace infrastructure. This commit also reverts all constructed()
functions to use assert again.
Replace all g_assert_not_reached() in app/core/ by g_return_if_reached()
or g_return_val_if_reached(). GIMP may handle a lot of creative work,
sometimes unsaved for hours. We should not just crash on purpose.
g_assert*() could theoretically be turned off on a glib build, but this
is nearly never done, and is not a solution either (actually it is
probably even worse because the broken code would just continue on a
forbidden path). It is much better to return with a warning on such
forbidden code paths, allowing someone to report a bug without
experiencing a crash and data loss.
For now, I only took care of g_assert_not_reached() inside app/core.
More g_assert*() code should be replaced.
Note: assert are acceptable in plug-ins though, but not in the main
executable, unless absolutely necessary (something happening so bad that
crash is better than continuing).
