Well, i _was_ going to defend the `Array#join` method for being the simplest and not being used in a hot part of the code (only for error reporting as of now). But [this quick](http://jsperf.com/repeat-string-n-times) jsperf makes it look _really_ bad; even compared with a naive implementation.

So well, i'm adding it mostly because it's in the helpers file, and it could be used anywhere else. The 1.5.0 release added quite a bit of performance overhead to the compiler, so there probably are other spots were we'd better optimize. But better use a profiler to find them.