hal_signal.pyx:  fix Signal error message and __repr__
hal_ring.c:  add ring name to error messages
debian/control:  add python-nose deps
Refactor nosetests

- Run all tests with one command
  - Overall results on bottom line
  - Reduce realtime setup/teardown time
- Provide examples for future test authors
  - Use `nosetest.assert_*` functions
- Simplify test writing where possible
  - RTAPITestCase class makes RTAPI connections trivial
  - Reduce interaction between tests with HAL check function
    - FIXME:  how to run this automatically between modules?
- Adopt proboscis with hierarchical test dependencies
  - Tests may be ordered
  - Skip tests whose dependencies fail