NormaliseToMonitor failing for MARI data

[mantid-builder]

Original Reporter: Russell Taylor

The algorithm checks that the specified detector is actually a monitor, and throws if not. This is a bit harsh - it means that the algorithm fails if the instrument is not fully specified, even though the algorithm itself doesn't need instrument information.

There's also a problem with the MARI instrument when loaded - it's losing the monitors.

[mantid-builder]

This issue was originally trac ticket 879