New optimisations for long raw strings in C++ Mode.

[Alan Mackenzie]

Hello, Lars, hello, Emacs.

I've just committed some optimisations to the savannah master branch
which should speed up the handling of long C++ raw strings in an Emacs
where font-locking is fully working.

On a megabyte long raw string in a normal build on a reasonably modern
machine, the response is slightly sluggish, but not unreasonable to
somebody who prefers correct fontification to instant response.

-- 
Alan Mackenzie (Nuremberg, Germany).