FIXED: tokenizing adjacent operators

FIXED: tokenizing adjacent operators

Make Sweep's Prolog tokenization functions more careful in their
handling of unrelated adjacent operators.  This fixes an issue that
affects term-based movement commands and other commands that rely on
'sweeprolog--forward-sexp' and friends.

* sweeprolog.el (sweeprolog-next-token-boundaries)
(sweeprolog-last-token-boundaries): Fix handling of
adjacent (distinct) operators.

* sweeprolog-tests.el
(forward-sexp-with-adjacent-operators): New test case.