Nobody has them anymore, and they are deprecated in GTK+ 3.x. This
also fixes all conflicting mnemonics except those I missed, but we can
fix them now.
Change GimpFileDialog's file-procs properties to enum
GimpFileProcedureGroup and get them via the newly added API. Set
properties common to all dialogs in the parent class.
file-procedure.[ch] is gone and its functions moved to
GimpPlugInManager where they belong (the manager keeps around the
lists of load, save and export procedures).
Utility functions from file-utils.[ch] that have nothing to do with
image files moved to core/gimp-utils.[ch].
The code refactoring allows better readability which will allow in turn
to add more complex specific features making good use of the save/export
split concept.
