Add -e to exec single test in shell

This is super-useful as a debugging tool.  I've really enjoyed having it and miss it when it's gone.  Current problems making this a work-in-progress:

* The exit status of the test is not reflected in the shell.  This arises because currently `-e` does not use a true exec, instead it runs the test within the normal pipeline and simply turns off post-processing of the output.  This is good for seeing the output but is a bit of a lie.

* No tests!