Start using throw in abort
Start using throw in abort

And this is a first pass at how to combine catch/throw with the other R
stack frame words.

Right now throw unwinds as long as the frame pointer is non-zero and
uless than the catch frame. This looks clunky but seems to work.

There are at least two options for change/improvement:

(1) Make catch/throw more like the rest of R frame words; that is, any
catch frames creates would last until the word in which they are defined
exits, rather than lasting only for the execution of the *one* following
word.

(2) Make catch frames a type of R frame and link them into the other R
frame list, rather than having a separate, parallel list of catch
frames.

I'm tempted to try both of these, actually...

nickhen/muforth,nickhen/muforth