[m-dev.] nostream/stream twin predicates in io.m

[Zoltan Somogyi]

The io.m module contains many twin predicates which differ
only whether they take an explicit stream argument. At the moment,
the two versions are usually commented separately (i.e. there are
two explanations of what the predicates do, differing only minimally),
and they are often not even next to each other (e.g. read_char/3
is declared on line 136, whereas read_char/4 is declared on line 223).

I propose to put both the declarations and the definitions of twin
predicates next to other, with a single shared and appropriately
generalized description.

I am pretty sure there won't be any objections, but I don't want to start
while anyone has any outstanding changes to io.m, since those would probably
conflict with this. Can people please reply saying whether they do or not?

Zoltan.