Add Rubinius 2.2.6.

Fixes #517

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.

Closes #514

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/

Added a JRuby 1.7.11 recipe.

Fix Java 7 detection

Java on most (all?) platforms directs `-version` output to STDERR.

Add mruby 1.0.0.

Update MagLev branch from master-1.9 to master

Leaves rubies >= 2.0 vulnerable to CVE-2013-6393

Ensures that color is off if the stderr stream is not a terminal

Require Java 7 for jruby-9000-dev.

Add support for rbx-2.2.5

Add JRuby 9000 snapshot.

This should plug the vulnerability to CVE-2013-6393 (and fix #504)
that can still occur in certain systems: If the ruby build process
couldn't find a libyaml that worked, it would build its own vendored
libyaml, which was 0.1.4 (and is vulnerable).

Instead, specify that the build always should install the latest
libyaml & build against that.