Squashed 'rbenv/plugins/ruby-build/' changes from c819790..3545e25

3545e25 Merge pull request #614 from sstephenson/rbenv-plugin-definitions
e567eab Merge pull request #615 from hone/ruby-1.9.2-p330
6eec23d add ruby-1.9.2-p330
78bc846 Auto-discovery of build definitions from rbenv plugins
6847c47 Add rbenv-install tests
f6e78a4 Merge pull request #613 from sstephenson/definition-paths
f118b17 Extra definitions paths via RUBY_BUILD_DEFINITIONS
ff75ca7 Support changing RUBY_BUILD_ROOT
4e2177d Add test for ruby-build definitions
223f0a5 Merge pull request #603 from wjordan/patch-1
70d8e39 Add link to suggested build environment to README

git-subtree-dir: rbenv/plugins/ruby-build
git-subtree-split: 3545e2595de3267918929853fe8a6f57150854b6
Merge commit 'bc871954a22f13ea451d89658e9a9ace76e2487e'

Pull ruby-build to `rbenv/plugins/ruby-build`.