[R6RS] naming convention for procedures

[Anton van Straaten]

I wrote:
> I notice that the "Entry format" section (3.1) does not list "proc" or 
> "procedure" as a naming convention which implies a type restriction. I'm 
> thinking it should.
> 
> Currently, both "proc" and "procedure" are used for this purpose in 
> different places - "procedure" most notably in arithmetic and hash 
> tables.  R5RS used "proc" for e.g. map and for-each (and similarly 
> didn't mention it in the "Entry format" section.
> 
> I'm going with "proc" for the stuff I'm responsible for, until I hear 
> otherwise.

P.S. I forgot that "if a parameter name is also the name of a type, then 
the corresponding argument must be of the named type."  That would argue 
for using "procedure".  Either way, it should probably still be listed 
explicitly, if we're going to list other base type names.

(I notice that R5RS only listed names that were not the name of a type.)