Upgrade to Ruby 1.9

[jfirebaugh]

I've just done a quick test of the full relation API, and 1.9.3 was twice as fast as 1.8.7:

https://gist.github.com/3933830

Upgrading to 1.9 would give us significant performance improvements without code changes or porting more of the API to C++.

[tomhughes]

This is an operational issue so not appropriate for this issue tracker.

For the record I have started making preparations for moving the production instances to run on ruby 1.9 and the dev instances are already doing so as a test bed.