Exposing more Instrument methods to python

[peterfpeterson]

People wanted to know what filenamethe IDF came from in python. This exposes that information.

There is no associated issue.

To test:

The additional unit test shows a great example.

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[RichardWaiteSTFC]

Looks like this doc string for setter is duplicate of getter.

Just out of interest, it looks like setting a different filename doesn't actually re-load the IDF (like calling LoadInstrument) - it looks like it just updates m_filename)

mantid/Framework/Geometry/src/Instrument.cpp

Lines 845 to 850 in 789921c

	void Instrument::setFilename(const std::string &filename) {
	if (m_map)
	m_instr->m_filename = filename;
	else
	m_filename = filename;
	}

so could exposing this to python could lead to problems? Depends on what you want to use this for I guess!

[peterfpeterson]

The SNAP team is overwriting the instrument file after doing a subsampling to make the instrument effectively have giant pixels.

[RichardWaiteSTFC]

So is this grouping neighbouring pixels or similar? Not sure what the benefit of having a separate IDF is (when you group detectors, e.g. when focussing it just keeps track of the detector IDs contributing to each spectrum), but obviously I'm not familiar with SNAP stuff! My one query would be does it make sense to be able to set the filename when it could be out of date with the IDF loaded (assuming LoadInstrument set this m_filename)?