Add MAKE_INSTALL_OPTS for packages

Allows for passing environment variables specifically to the "make install"
step of package building.

This can be helpful for providing a different DESTDIR= to a ruby install from
the --prefix that is used
Add tests for RUBY_MAKE_INSTALL_OPTS=
Add mention of RUBY_MAKE_INSTALL_OPTS in README
Add MAKE_INSTALL_OPTS configuration option
Add test for MAKE_INSTALL_OPTS

Also fix the ordering of make install arguments
Fix install file mode for files in share/

install(1) defaults to file mode 0755 which is inappropriate for Ruby
definitions
Test that files in `share/` get installed w/ mode 644
Merge branch 'install-mode'

Closes #483
Merge pull request #493 from eric/add-make-install-opts-variables

Add MAKE_INSTALL_OPTS for packages
Add Rubinius 2.2.4
Update libyaml to version 0.1.5

Closes https://github.com/sstephenson/ruby-build/issues/499.
ruby-build 20140204
Add warning about CVE-2013-6393 to CHANGELOG [ci skip]

Actually resolves https://github.com/sstephenson/ruby-build/issues/499.
Install libyaml 0.1.5 for 2.x rubies also

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.
Add JRuby 9000 snapshot.
Merge pull request #505 from chrisseaton/jruby-9000-dev

Add JRuby 9000 snapshot.
Added support for rbx-2.2.5.
Merge pull request #506 from anthonator/master

Add support for rbx-2.2.5
Make whitespace consistent across build definitions
ruby-build 20140210