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
Makefile:  userpci:  always install headers

Fixes #298

This updates the previous attempt in #333.  It's a hack to avoid
templating `debian/machinekit-dev.install`.
Don't install Cython shared objects into /usr/lib

Another example of the inflexibility of this build system
Hack to get unit tests working from debian packages

This patch modifies the realtime system so that it can run in a
`${DESTDIR}` directory so that unit tests can be run during package
builds, where Machinekit is installed under `${DESTDIR}${prefix}`.