Workaround for JRuby failure [WIP]

As of 

- https://github.com/jruby/jruby/issues/1243 and
- https://github.com/jruby/jruby/issues/1789,

there might be a regression in JRuby 1.7.x, while JRuby 9000 works
just fine. 

(Side note: please don't branch off this commit as long there is
an Work-In-Progress tag. I will force push some minor changes
when fiddleing with Travis...)