Added reporters.

ert-runner now supports an extensible reporter architecture with
different styles of output. The default reporters are a copy of
the normal ERT code, and a short dot reporter.
Added a --quiet option to capture test output.

This option will prevent messages from a test to be emitted unless
the test fails, in which case the full output will be shown.

This commit also cleans up messages from reporters, and unifies
error messaging.
Use correct ert-runner in tests.

Previously, the ert-runner binary used was the one installed from Melpa,
but we obviously want to test the local one.

Add {ERT-RUNNER} as a replacement for the path to the local binary.
Should see error, not output.
This is the output from the dot reporter, not ert.
Clean up the message capturing code.

We now don't go quiet unless we're without an interactive session.
Also, the whole capturing code was cleaned up considerably, now
avoiding a roundtrip through ert-runner-print for normal princ
behavior.
Merge branch 'reporter'