JRuby support

[fatum]

Hi to all!

Einhorn cannot run on jruby due to a lack of fork. Can i make a patch for that? I propose replace fork + exec by posix_spawn for MRI and spoon for jruby.

If einhorn will support jruby it can be proposed for puma instead its cluster mode :)

• posix_spawn – http://www.oracle.com/technetwork/server-storage/solaris10/subprocess-136439.html
• a fork/exec replacement for jruby – https://github.com/headius/spoon
• using spoon in foreman – https://github.com/ddollar/foreman/pull/140/files

[fatum]

UPD: for JRuby server sockets are not seamless on restart, they must be closed and reopened. JRuby have no way to pass descriptors into a new process that is exposed to ruby