Support emitting 1.9 Symbol keyword Hash syntax when pretty printing Hashes
Ruby 1.9 first introduced support for keyword Hash syntax for simple Symbol keys. However, Hash#inspect and pp do not emit the same syntax when printing Symbol keys. This patch adds support for "foo: " syntax to the pp_hash method, iff the key is a Symbol and does not contain any spaces or special characters. While the patch is probably not perfect, I hope to start a discussion.