Better filter name handling

Add some better filter name validation, and be a little less strict about what constitutes a valid name.

This is due to my thinking 'hcm-writes' would be a valid name, but it wasn't. And I couldn't immediately figure out why I was getting errors. The filter should have failed earlier.


Sidenote: the TODO note in the first commit is talking about a different kind of validation. Just another thing that bit me recently.