Run test:cxx in rvmsudo instead of sudo because it needs Ruby libraries.
Have test:install_deps install the latest rack gem.
Do not test Rails 2.3 on Travis because Rails 2.3 doesn't support RubyGems 2.0.
Revert "Temporarily enable some debugging statements for Travis."

This reverts commit 1a1c46c9f6cce91b259f30dae7d03fb2094efd68.