Upgrades rubygems for 1.9.1: 1.3.5 -> 1.3.7
Update share/ruby-build/rbx-2.0.0-dev

Rbx 2.0.0-dev need yaml install like rbx 2.0.0-rc1
Added a recipe for JRuby 1.7.2.
Merge pull request #262 from nirvdrum/add_jruby_1.7.2

Added a recipe for JRuby 1.7.2.
ruby-build 20130104
Definition for ruby 2.0.0-rc1
Merge pull request #265 from mariochavez/master

Add definition for Ruby 2.0.0 rc1
Add 1.9.3-p374
Merge pull request #269 from sorah/193p374

Add 1.9.3-p374
Invoke chmod for group or world writable directories only
ruby-build 20130118
Support selection of 'make' tool via environment variable
Merge pull request #272 from onibox/make-env-var

Support selection of 'make' tool via environment variable
Merge pull request #271 from nobu/master

No needs to chmod all directories.
Update examples
Allow plugins to run code before and after the installation process
`rbenv install` with no arguments defaults to `rbenv local`
Confirm reinstalling already-installed versions unless invoked with --force
Move MAKE default near the others
Ensure $MAKE is quoted