[do_jdbc] Compilation of Java extensions no longer requires buildr by default
[do_jdbc] Compilation of Java extensions no longer requires buildr by default

* Instead compilation and packaging now calls javac/jar directly.
* Obviates requirement for buildr gem to be installed, although
  a separate task has been added to build using buildr.
* Code to discover JRuby classpath copied from ActiveRecord-JDBC
  project.

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

simonkro/do_mysql,simonkro/do_mysql,simonkro/do_mysql