[ ] { }

[Jonathan Rees <Rees at YALE>]

I want to change the status of the four special characters [ ] { and }
in the standard T syntax to be no longer defined as "constituent" (i.e.
extended alphabetic) characters.  This means that where before one
could write e.g. [FOO] to notate a symbol whose pname is "[FOO]", one
would now need to say \[FOO\].

For now, they won't be defined to be anything else (I haven't committed
to anything), it's just that it would be nice for people to not depend
on their alphabeticness, or at least to be explicit in setting their
syntax, e.g. with
 (SET (SYNTAX #\[) (SYNTAX #\A))).

Note that at some point in the future one will probably need to specify
special read syntax in a file's HERALD somehow, rather than in random top-level
 (SET (SYNTAX ...) ...) forms.  This facility still under development.

Any serious objections to this change?  I realize that "locking down"
special characters for weird syntax is to be avoided, so I could probably be
talked out of it.