Added a JRuby 1.7.11 recipe.
Merge pull request #515 from nirvdrum/jruby-1.7.11

Added a JRuby 1.7.11 recipe.
Add support for JRuby 9000 bundled with the Graal VM

JRuby 9000 (the next major release) includes a backend that supports a
new JVM JIT compiler called Graal. Graal is based on OpenJDK but hasn't
been released yet.

http://openjdk.java.net/projects/graal/
Add test for JRuby+Graal
Merge branch 'graal'

Closes #514
ruby-build 20140225
Fix typo in CHANGELOG [ci skip]
Fixes check for user-specified definition

Better to use -f than -e to check for a user-specified definition file.
With -e, if the user accidentally types the name of a directory (or, far
less likely, a device file) with the same name as the Ruby they're
trying to install, they end up with ruby-build doing absolutely nothing
at best, or an error message that could be pretty confusing at worst.
Merge pull request #518 from dpoggi/better-user-specified-definition-check

Fixes #517
Add Rubinius 2.2.6.
Merge pull request #523 from brixen/master

Add Rubinius 2.2.6.
Add installation instructions for Arch Linux

Closes https://github.com/sstephenson/ruby-build/issues/526.
Revert "Add installation instructions for Arch Linux"

This reverts commit 6cf348e426cd210b4637bf22db12da6a62f8a478. See
https://github.com/sstephenson/ruby-build/issues/526#issuecomment-37889552.
Fix re-downloading tarball when destination file already exists

Previously, curl and wget were instructed to try to resume the download
if the destination file already exists. This is supposed to be done via
the "Range" HTTP header, but doesn't work well with CloudFront:

    HTTP server doesn't seem to support byte ranges. Cannot resume.

CloudFront is supposed to support ranges, so I don't know what's going
on here. It might be failing only in case the existing file is a fully
downloaded tarball?

In any case, this disables resuming downloads and resorts to simply
re-downloading the tarball always, overwriting the existing file.

Fixes #487
Avoid re-downloading if there's a valid tarball in build location

If there already exists a valid tarball in the build location, e.g. as
artefact of a previous install using `--keep`, don't re-download the
file, as there is no need.

References #487
Merge branch 'no-resume-download'
Update libyaml to 0.1.6

Security fix for CVE-2014-2525

Advisory: http://www.ocert.org/advisories/ocert-2014-003.html
Merge pull request #534 from josacar/security-CVE-2014-2525

Update libyaml to 0.1.6
Add `rbenv install --skip-existing <VERSION>` option

The `-f` option allows for forcing installation of versions that already
exist in the environment. If that option isn't used, then an interactive
prompt is created which causes problems for non-interactive execution of
the command.

This change adds the `-s/--skip-existing` option to not install versions
that already exist, while still exiting as success.

Closes #543
2.0.0-p451 should use libyaml-0.1.6 too