update JRuby to 1.7.16.1

Also updates some other dependencies:

  * guava
  * rb-inotify
  * maven-plugin-api

and plugins:

  * gem-maven-plugin
  * maven-plugin-plugin

and require at least maven 2.2.1 to build (which was required implicitly
anyway, but lets be clear about it)

close #14
Merge pull request #1 from mprins/jruby179

update JRuby to 1.7.16.1