swift234

Add a tool to generate DOT graphs from a set of .swiftdeps files.

This produces graphs showing dependency relations between files, according to the
.swiftdeps files generated from a build. Solid lines

  % analyze_deps.rb path/to/build/*.swiftdeps

I used this locally to generate pretty pictures last year. Unfortunately, the DOT
tools don't scale very well to huge graphs.

Swift SVN r29805