For any other value, redisplay all mode lines (the number used is then only
used to track down the cause for this full-redisplay).
+ Since the frame title uses the same %-constructs as the mode line
+ (except %c and %l), if this variable is non-zero, we also consider
+ redisplaying the title of each frame, see x_consider_frame_title.
+
The `redisplay' bits are the same as those used for
windows_or_buffers_changed, and setting windows_or_buffers_changed also
causes recomputation of the mode lines of all those windows. IOW this