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
Implements memoization for ancestor matching.

This yields a log(#ast_nodes) worst-case improvement with matchers like
stmt(unless(hasAncestor(...))).

Also made the order of visitation for ancestor matches BFS, as the most
common use cases (for example finding the closest enclosing function
definition) rely on that.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177081 91177308-0d34-0410-b5e6-96231b3b80d8