[R6RS] Promises extensions

[Michael Sperber]

The description of `delay' and `force' still mentions the possibility
that some implementations might implement variations of implicit
forcings.  Do we leave that in?  It doesn't seem to do much harm
except take up space, but I'm not aware of any existing
implementations that actually do this.

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla