Better implementation of JavaScript === and !== operators.

Summary:
Now based on token merging. Now they are not only prevented from being
split, but are actually formatted as comparison operators.

Reviewers: djasper, klimek

Reviewed By: klimek

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D2240

llvm-svn: 195354