Rufflewind authored May 20, 2017 and Ben Gamari committed May 20, 2017

rwbarton pointed out that tab expansions can affect the column numbers
of subsequent characters, so a unstateful map + zip won't do.  This
commit hopefully fixes that.  It also adds a test for this particular
case.

Test Plan: validate

Reviewers: bgamari, rwbarton, austin

Reviewed By: bgamari

Subscribers: dfeuer, thomie

Differential Revision: https://phabricator.haskell.org/D3578