1.8 series ruby needs to pull in -rrbconfig for RbConfig to work.
Merge pull request #1556 from cwgem/rbconfig-1.8-fix

1.8 series ruby needs to pull in -rrbconfig for RbConfig to work.
fix detecting if osx homebrew is writable by user, update #1555
Merge branch 'master' of github.com:wayneeseguin/rvm