runtime accel changes

[Ryan Lortie <desrt desrt ca>]

hi,

I recently wrote a patch[1] to re-enable accel labels in GtkMenu 
generated from GMenuModel.  They got lost in the shuffle during some 
related recent changes.

Essentially, the new approach means that the accel='' attribute of each 
menuitem directly determines what the accel label will be (instead of 
doing the lookup in the accelgroup).

The most noteworthy impact of the patch (and the topic of this email) is 
the strong implication that we will no longer support runtime changing 
of accel keys.

It's my personal opinion that runtime changes to accels have resulted in 
some rather complicated code in Gtk and we'd be better off without this 
feature.  Additionally, the feature is disabled by default for quite 
some time because enabling it results in lots of bug reports from 
confused users.

In the future we will likely gain some sort of action-database/factory 
functionality (to replace the other half of GtkAction -- creating 
proxies).  I imagine accels will be registered with this database at 
application initialisation time.

I could see a hook (like a keyfile in ~/.config/ somewhere) that allows 
advanced users to adjust their accels.  An app restart would be required.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=683738