Correct indentation of ids in a C++ enum after a protection keyword.

Correct indentation of ids in a C++ enum after a protection keyword.

Also correct the misfontification of the last enum identifier.

* lisp/progmodes/cc-engine.el (c-forward-keyword-prefixed-id): setq
c-last-identifier-range to nil to ensure that only types recognized by this
macro are set for fontification as types.
(c-backward-typed-enum-colon): Function renamed from
c-backward-colon-prefixed-type.  On finding a colon in the backward search,
check it is preceded by an identifier rather than a keyword.