MRI 1.9.3-p194 YAML parsing performance regression

If you have any Ruby code that relies on YAML parsing, you should avoid MRI 1.9.3-p194 as the bundled up version of psych (v1.3.2) is approx. an order of magnitude slower than v1.2.2.

Trunk of MRI 1.9.3 contains psych v1.3.4 which is back to normal performance.