Fixed issue causing java file not found exception

[danlynn]

Fixes an issue where a java file not found exception would occur if the Inline.directory did not exists already before attempting to build inline java source. The RubyInline gem will automatically create the ~/.ruby_inline dir just fine. However, if running under JRuby, the ~/.ruby_inline/jruby-1.8 dir would not be automatically created and the java exception would be thrown. Test this by deleting the ~/.ruby_inline/jruby-1.8 dir and running any java_inline test code.

I implemented this fix with the mirah_inline and scala_inline variants too.

I did not update the gemspec info. I figured that would be up to you.