jruby: implement restart mechanism

One can now `touch tmp/restart.txt' in the plugin root directory
to reload a ruby plugin. This is useful to hotswap the code.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
jaxrs: avoid double-committing plugin responses

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
osgi: optimize imports

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>