33% speed up in CC Mode scrolling.

[Alan Mackenzie]

Hello Martin, Eli, John, and Emacs.

I've just committed b76385c05076f0adaf7cf89d0ed95dfe5e8570e0 to the
master branch.  This takes some code out of CC Mode's font-locking's
hottest loop and puts it back in again in a place where is gets called
less often.

This speeds up CC Mode's scrolling (as measured on our favourite file,
xdisp.c) by about one third.  There may be scope for further optimisation
of this code.

This is a substantial and worthwhile, although not spectacular, speed up
of CC Mode.

-- 
Alan Mackenzie (Nuremberg, Germany).