When preprocessor generates errors, they should be visible in runner.

1) lunch karma start
2) have preprocessor which causes an error msg
3) run karma run
4) notice that the error messages does not show up in the karma run window.

Reproduce the problem with `karma start`, a preprocessor that emits an error, and `karma run`, then trace where that error is handled and where the runner window output is assembled. Done means the preprocessor error is visible in the `karma run` window and the behavior is covered by a regression test.

Written by the indexing model from the issue text.