Registration function probing loads Automation Add-Ins into .xll AppDomain

When calling xlfEvaluate to probe whether other .xll add-ins expose the magic function registration function, Excel loads registered Automation Add-Ins into the .xll AppDomain.

This may cause the Automation Add-Ins to misbehave.

We should try to find another way to probe for this function - for Excel-DNA add-ins we might look for the 'fixed' dll export. But what about other .xll frameworks that also support IntelliSense, like PyXLL?

The initial discussion was here: https://groups.google.com/forum/#!topic/exceldna/c1_7spWlOJQ