Cope better with C++ and Objective-C protection keywords in class declarations

Cope better with C++ and Objective-C protection keywords in class declarations

This fix fixes the fontification of a method inside a class at the time it is
typed, when there is a protection keyword clause preceding it.

* lisp/progmodes/cc-engine.el (c-forward-keyword-clause): Handle protection
keywords.
(c-looking-at-decl-block): Avoid scanning forward over protection keyword
clauses too eagerly.

* lisp/progmodes/cc-langs.el (c-protection-key c-post-protection-token): New
lang defconsts and defvars.

* lisp/progmodes/cc-mode.el (c-fl-decl-start): When we encounter a protection
keyword following a semicolon or brace, move forward over it before attempting
to parse a type.