Fix fullstop detection in presence of dot character literal

Fix fullstop detection in presence of dot character literal

This fixes an issue where the character "0'." in a clause body would
confuse clause boundaries calculation.

* sweeprolog.el (sweeprolog-end-of-top-term): Make sure fullstop have
punctuation syntax class (otherwise it's part of a character literal).
* sweeprolog-tests.el (end-of-top-term-with-dot-char-literal): Test it