add .jrubydir info to embedded gems in gems.jar

[mkristian]

only with this .jrubydir in each directory the directory inside the jar is working over ALL classloaders. i.e. just add GEM_PATH=uri:classloader:// to load those gems via the classloader directly.

there is command witj jruby itself (version 1.7.13+):

https://github.com/jruby/jruby/blob/master/core/src/main/ruby/jruby/commands.rb#L16

which can be used for this tasks (if possible)

related to: jruby/jruby-maven-plugins#64

--- Want to back this issue? **[Post a bounty on it!](https://www.bountysource.com/issues/7621187-add-jrubydir-info-to-embedded-gems-in-gems-jar?utm_campaign=plugin&utm_content=tracker%2F136961&utm_medium=issues&utm_source=github)** We accept bounties via [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F136961&utm_medium=issues&utm_source=github).