Closes #883

http://rubinius.com/2016/01/07/rubinius-3-0-the-third-epoch/

New urls for old Rubinius versions and unavailable versions removed

Add JRuby 9.0.5.0

Leverage assertion test helpers

Add JRuby 1.7.24

Checksum refactor

Bash 3 doesn't have associative arrays. Use variable indirection to
save various checksum algorithm support results. `printf -v` can save
the output to a variable, whose name is itself stored in a variable

- Remove unnecessary HAS_X_SUPPORT variables
- Merge conditional for unsetting mirror-url
- Memoize has_checksum_support function

Explicitly specify destination refspec

`git push <remote> HEAD` is documented to push current branch to
same-named branch on the remote

Leverage assert_success helper

rbenv ensures RBENV_ROOT is set for us

Clean up usage documentation

And separate test body into arrange-act-assert blocks via newlines

Update rubinius builds openssl from 1.0.1q to 1.0.2e