Multi-line comment alignment

Summary:
Aligns continuation lines of multi-line comments to the base
indentation level +1:
class A {
  /*
   * test
   */
  void f() {}
};

The first revision is work in progress. The implementation is not yet complete.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D541

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177080 91177308-0d34-0410-b5e6-96231b3b80d8