LoadMD + FileBackEnd: error messages when ticking combinations of options

[mantid-builder]

This issue was originally TRAC 11604

Original Reporter: @FedeMPouzols

This is really minor, just noting it down here. It could be fixed when any other changes/additions are done in LoadMD, FileBackEnd and friends.

To test the FileBackEnd property of the algorithm LoadMD, I'm going to load the file
SEQ_MDEW.nxs (available in the system tests data).

• If I select FileBackEnd and BoxStructureOnly but not MetadataOnly, an error (exception) will tell me: Both BoxStructureOnly and fileBackEnd were set to TRUE: this is not possible. That is correct. You can do this with the algorithm dialog or:

Load('SEQ_MDEW.nxs', OutputWorkspace='tws', FileBackEnd=1, BoxStructureOnly=1)

• But if I select FileBackEnd and MetadataOnly, but not BoxStructureOnly, the same throw will tell me the same Both BoxStructureOnly and fileBackEnd were set to TRUE: this is not possible., even though I didn't selected BoxStructureOnly.

Load('SEQ_MDEW.nxs', OutputWorkspace='tws', FileBackEnd=1, MetaDataOnly=1)

It will tell you: Both BoxStructureOnly and fileBackEnd were set to TRUE: this is not possible.

This error message is not correct and could be confusing.

This seems to come down to how m_BoxStructureAndMethadata is used in the if that throws that exception.