Allow iruby to work with ruby 1.8.7

I have an older Rails application I need to support, so I'd like iruby to work with Ruby 1.8.7. Right now, iruby only works with Ruby 1.9. This patch is at least a first step to giving support for Ruby 1.8.7. There are 2 changes made:

1. Use a backport for the uuid member of SecureRandom (in Ruby 1.9 but not 1.8)
2.  Change all the uses of the new 1.9 hash syntax to the old 1.8 'rocket' notation, i.e. "=>".

Neither of these changes break 1.9, they just add support for Ruby 1.8.7.