Merge remote branch 'origin/feature/6874_remove_registerAlgorithm_function'
Merge remote-tracking branch 'origin/bugfix/7581_plot_assoc_crash'
Merge remote-tracking branch 'origin/bugfix/8001_getBaseInstrument'
Resurrect test for Python instrument export.

It had been implemented incorrectly and it looked as if it was passing
when it wasn't.
There was also a bug with the getReferenceFrame import that this also
caught and fixed.
Refs #8000
Solve compiler warnings about const casting noted by gcc 4.7.2

Note technically related to this ticket but while we're improving tests...
Refs #8000
Merge branch 'bugfix/8000_python_instrumenttest' into develop