(19864) num2bool match fix

(19864) num2bool match fix

This is a bit more heavy-handed than I might like, but it does appear to
do the right things:

* accepts numeric input appropriately, truncating floats
* matches string input against a regex, then coerces number-looking
  strings to int
* makes a best effort to coerce anything else to a string, then subjects
  it to the same treatment
* raises an error in the event of incorrect number of arguments or
  non-number-looking strings

I've also included some additional unit tests.