Update ruby to 1.9.2 on Ubuntu 11.10

$sudo apt-get remove ruby rubygems ruby1.8 ruby1.8-dev ruby1.8-full
$sudo apt-get install ruby1.9.1-full
$sudo update-alternatives --set ruby /usr/bin/ruby1.9.1
$sudo env REALLY_GEM_UPDATE_SYSTEM=1 gem update --system