* tparam.h: New file.

* tparam.h: New file.

* term.c, tparam.h: Include it.
* deps.mk (term.o, tparam.o): Depend on tparam.h.
* term.c (tputs, tgetent, tgetflag, tgetnum, tparam, tgetstr):
Move these decls to tparam.h, and make them agree with what
is actually in tparam.c.  The previous trick of using incompatible
decls in different modules does not conform to the C standard.
All callers of tparam changed to use tparam's actual API.
* tparam.c (tparam1, tparam, tgoto):
Use const pointers where appropriate.