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.
1.9.3 builds with performance patches.
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