Initial implementation of "abort-redisplay" feature

Initial implementation of "abort-redisplay" feature

* src/xdisp.c (update_redisplay_ticks): New function.
(init_iterator, set_iterator_to_next): Call
'update_redisplay_ticks'.
(syms_of_xdisp) <max_redisplay_ticks>: New variable.
<list_of_error>: Remove 'void-variable': it is no longer needed,
since 'calc_pixel_width_or_height' can no longer signal a
void-variable error, and it gets in the way of aborting
redisplay via 'redisplay_window_error'.