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