(font-lock-extend-after-change-region-function):

(font-lock-extend-after-change-region-function):
Rename from font-lock-extend-region-function.
(font-lock-extend-region): Remove by inlining at call sites.
(font-lock-after-change-function): Don't needlessly round up to a whole
number of lines.
(font-lock-extend-jit-lock-region-after-change): Be more careful about
the boundary conditions and the interactions between the various ways
to extend the region.