Try to better explain why a localized exception message could not be retrieved

[jng]

Sometimes a localized exception message fails to be retrieved because due to an internal coding error, an exception was thrown with no or insufficient arguments to properly format the required exception message.

This error is currently discarded and the generic "failed to retrieve message" message is returned instead.

Where possible we should try to capture the source error and include this as the reason for the "failed to retrieve message". This will at least give internal developers a clue to where an exception is thrown without the required message arguments.

[jng]

This is actually harder than initially thought due to the exception message formatting code being in MgException itself and the formatting code potentially throwing MgExceptions itself and how to avoid a super-recursively nested explanation error message as a result.

Milestone removed.