Correctly indent with tabs when whitespace starts from the column not divisible by TabWidth.

Summary:
The width of the first inserted tab character depends on the initial
column, so we need to handle the first tab in a special manner.

Reviewers: klimek, djasper

Reviewed By: klimek

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1763

llvm-svn: 191497