- Changed PathDiagnosticPiece::getLocation() to return a PathDiagnosticLocation

  instead of a FullSourceLoc. This resulted in a bunch of small edits in various
  clients.
- Updated BugReporter to include an alternate PathDiagnostic generation
  algorithm for PathDiagnosticClients desiring more control-flow pieces.

llvm-svn: 68193