bug#56682: feature/improved-locked-narrowing 9dee6df39c: Reworked locked narrowing.

[Gregory Heytings]

> Hmm... I'm probably missing something, but doesn't 
> narrowing_locks_remove permanently removes the lock from the restriction 
> in the buffer?  And if so, don't we want to restore the lock after 
> whatever we need to do in a widened buffer is done?

Yes: that's what the "record_unwind_protect (save_restriction_restore, 
save_restriction_save ());" does.  The two places where 
'narrowing_locks_remove_in_current_buffer' is not preceded by that 
statement are the two places where we indeed don't want to restore the 
restrictions after widening: Ferase_buffer and Fcall_process_region.