emacs gyp-mode: Fix very slow string tokenization problem. 

Gyp-mode uses forward-sexp which can be very slow on Emacs 24.3.50.1, 
making it appear that Emacs has crashed in certain situations.   Use scan-sexps
directly, instead.

Also, in recent Emacs versions, the comment delimiter is separately 
fontified with font-lock-comment-delimiter-face. Adjust the test 
code to ignore the differences between this and 
font-lock-comment-face. 

Based on patch by  John Knottenbelt <jknotten@chromium.org>

TEST=run-unit-tests.sh
Review URL: https://codereview.chromium.org/12732006

git-svn-id: http://gyp.googlecode.com/svn/trunk@1593 78cadc50-ecff-11dd-a971-7dbc132099af