Added the ability to see source context with each frame in the "crashlog"...

Added the ability to see source context with each frame in the "crashlog" command with the "--source-context" (-C for short to match grep) option.

Also made the symbolication of the crash logs more efficient when using the "--crashed-only" ("-c") option where only the crashed thread is symbolicated. We now only download the images for the frames in the crashed thread.

llvm-svn: 160160