In Mammography, it is possible for different modalities to end up in one study

[Ed McDonagh]

Issue discovered with 'Hologic' studies containing exposures from GE systems, and vice-versa.

Assumed at this stage to be due to the nature of importing from images using the mam.py routine attempts to 'add' new exposures to existing studies where accession numbers match.

Should be possible to add a check for matching the equipment too.

First reported by @LaurenceKing