numtest: add --silent and --verbose

To make travis-ci.org happy, make numtest print out a status report
every 60 seconds and silence after 100 warnings.

If there is more than 10 minutes of silence, travis-ci will abort the
test. Write a status message to keep tests alive (unless --silent).

If there is more than 4 megabytes of logs, travis-ci will kill the test.
Write only first 100 failure messages (unless --verbose).
Tweak .travis.yml

Disable email notifications, remove "branches" section which doesn't
work.