Report javascript errors that prevent specs from running.

[swistak]

This solution is a bit hackish. But allows us to forward console output
and errors from javascript to test runner.

There can be multiple errors, and each of them will get reported.

Also specs will be marked as failed which gives correct error status for CI

[swistak]

I've reworked solution to be completelly on side of javascript. Does not break tests anymore. But only reports one error.

[swistak]

Travis reports build as failed becouse it failed on rbx in 1.9 mode (dunno why, but master also fails). Other platforms passed.

[netzpirat]

This is great! Thanks a lot. I know that there are currently some problems with Rubinius, but I'm unsure what the problem is and I can't even install Rubinius on my local machine to investigate at the moment. Hope I can fix it next week and release a new version.