Test for correct usage of columnWidth in clang fixit hints.

Summary:
This test only works on systems capable of outputting UTF-8 encoded
text on the standard output (tested on linux and OS X, should XFAIL on windows,
if I haven't messed up the XFAIL line).

Reviewers: jordan_rose

Reviewed By: jordan_rose

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1607