[gforth] questions about callback#

[Reepca Russelstein]

callback# is used both at generate-time (in words used by
callback-gen) and at first-instantiation-time. If the two values don't
match, bad things happen (in my case, I attempted to pass a function
pointer pointing to address 14. Yikes).

Example:

c-library test
3 to callback#
c-callback used-rarely -- void
20 to callback#
c-callback used-frequently n -- void
end-c-library

' noop used-rarely .

Prints 8 for me - it tries to access the 19th callback of
used-rarely... seems that ccb-num should be set at generate-time
rather than setup-time.