JRuby specific system in core/util.rb

[Pepijn Van Eeckhoudt]

Does anyone remember why the jruby specific system workaround using FFI 
was done in core/util.rb? This has the annoying side effect on windows 
of bringing up a new console window for the subprocess everytime it is 
run. Seems to work fine with the non-jruby specific variant as well.

Pepijn