Set script’s working directory based on project/script path

For projects, the working directory will now be set to the project directory, if there is no project then the file’s directory is used, and if running an untitled document, the user’s home directory is used as a last fallback.

Related discussion at http://lists.macromates.com/textmate-dev/2013-May/014885.html
Use version 1.8 of ruby for bundle items

10.7 and 10.8 only include ruby 1.8, so all bundle items have been written to work with that. Optionally supporting ruby 1.9 and 2.0 is problematic as these versions are not fully backwards compatible.

#ignore
Merge branch 'master' of https://github.com/textmate/r.tmbundle

Conflicts:
	Commands/Run Selection:Document In R.tmCommand