Handle `parse-partial-sexp' landing inside a comment opener

Handle `parse-partial-sexp' landing inside a comment opener
	(Bug#13244). Also adapt to the new values of element 7 of a parse
	state.

	* progmodes/cc-engine.el (c-state-pp-to-literal): New optional
	parameter `not-in-delimiter'.  Handle being inside comment opener.
	(c-invalidate-state-cache-1): Reckon with an extra "invalid"
	character in case we're typing a '*' after a '/'.
	(c-literal-limits): Handle the awkward "not-in-delimiter" cond arm
	instead by passing the parameter to c-state-pp-to-literal.

	* progmodes/cc-fonts.el (c-font-lock-doc-comments): New handling
	for elt. 7 of a parse state.