Ensure system ruby is used for “RubyMate”

Ruby 2.0 will close non-standard file descriptor when calling Kernel#exec, which means that the file descriptor used for printing the stack trace is unavailable in our child process.

Ruby 1.8.7 does not accept any options to Kernel#exec so it doesn’t seem like we can make the script compatible with both versions of ruby (at least not with simple code).

This should avoid issue #21.

Related thread on mailing list: http://lists.macromates.com/textmate/2013-March/036014.html
make run focussed unit test work for shoulda tests
Allow methods to appear after {} without breaking indent
Make help command use APIDock.
Remove Ctrl-Shift-w keybinding (should call 'Wrap Selection' even in Ruby mode)
Make Ctrl-" toggle only between single and double quotes.

Treat %Q{...} as one of the 'more esoteric quote styles' (i.e. convert it to double quotes if Ctrl-" is used on it.
Fix invalid key binding that disables dead keys.

See http://lists.macromates.com/textmate/2012-September/035552.html
Simplify do...end snippet.

Make it easier to use for do...end blocks without block variable.
Simplify 'encoding: utf-8' snippet, use 'enc' as trigger.

utf-8 is the only encoding we use anyway, so no need to make it editable. And there should be no newline after the snippets, too.