Travis: Don't use --use-mirrors with pip.

It's been deprecated and I think we don't need it ;-)
Added sysdb(1) manpage and updated sysdb help output.
sysdbd(1): Fixed typo.
README: Added links to travis-ci and coveralls.
Travis: Don't use 'coveralls --verbose'.

coveralls reports work fine now, so we don't need this anymore.
Travis: Only run coveralls when using gcc.

We don't have any gcov information in any other case.