Default output is excessively verbose

[xldenis]

I've started porting my tools over to ui_test, but I find the default output to be excessively verbose: it systematically dumps the diff and the full stdout / stderr, could we include a version of the Text emitter which does not dump the full file contents? My stdout files are often ~20-30kloc long but with < 100 lines of diff, which makes the default status emitter fairly useless.

[oli-obk]

oh, yea that makes sense. We could add a flag to the Text emitter to just not dump the full output, but only the diff