ruby-build 20111030

• Add Ruby 1.8.7-p334
• Renamed the 1.9.4-dev definition to 2.0.0-dev to reflect the new
  version numbering scheme
• ruby-build now automatically displays the last 10 lines of the error
  log, if any, when a build fails
• Improve the GCC detection routines and add a more helpful error message for
  Xcode 4.2 users
• JRuby installation no longer requires the install prefix to exist
  first
• You can now pass $CONFIGURE_OPTS to the REE definitions
• Add JRuby 1.6.5
• Add Ruby 1.9.2-p180
• Add Ruby 1.9.3-p0