Removing rspec :version from Guardfile

Passing the version is now deprecated, and we are using version 2 as it
required anyway.
Removing pry-nav for Guard

pry-nav was throwing exceptions in resolving the shoes.gemspec every time Guard
would perform any checks. After asking, I've just removed it.

pry itself wasn't causing any issues I could see, so I've left that in place
for those that might want to use it.
Adding shoes-guard script

On OS X unfortunately we have to pass the -J-XstartOnFirstThread flag along to
JRuby and the JVM when starting up, otherwise the SWT tests fail badly. Even
worse, apparently setting that flag will cause other OS's to crash.

Everyone can use bin/shoes-guard to start up Guard, and those on OS X will get
the necessary flag set, while other OS's won't.
Call out dsl.rb -> swt/dsl_spec.rb
Missing spec/spec_helper