bundle install / update: libv8 (therubyracer) installation fails (with native extensions)

I recently wanted to update my gem bundle but ran into installation problems with libv8 (requirement for therubyracer): ``` Installing libv8 (3.3.10.3) with native extensions /usr/local/rvm/rubies/ruby-1.9.3-head/lib/ruby/site_ruby/1.9.1/rubygems/installer.rb:552:in `rescue in block in build_extensions': ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError) /usr/local/rvm/rubies/ruby-1.9.3-head/bin/ruby extconf.rb Checking for Python...*** extconf.rb failed *** Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options. ``` I have found the issue report on therubyracer github site and it suggests to uninstall and reinstall libv8, but this does not work on my Ubuntu 11.04 machine. Any ideas - or am I stuck with the old version for a while?