Begin improving JRuby compilation tasks
Begin improving JRuby compilation tasks

* JRuby extensions should now be cross-compilable when running
  compilation tasks under another Ruby interpreter (i.e. MRI).
* Other bits of cleanup. Fail gracefully if JRUBY_HOME not set.
* Warn that classpath and extension directory detection is more accurate
  when running tasks with JRuby interpreter.

Signed-off-by: Alex Coles <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@alexcolesportfolio.com>

simonkro/do_mysql,simonkro/do_mysql,simonkro/do_mysql