rename typeinfo

[David Grundberg]

Hello maintainers,

I've read at least 3 messages on octave-help confusing 'typeinfo' and
'class'.  I've helped these people, but I'm afraid there are others
incorrectly using typeinfo where they ought to use class.  The
documentation could be improved for typeinfo, but I think renaming it to
something else would be even better.  I suggest that we put a underscore
or something to it.  Like __typeinfo__.

Grundberg