(c-initialize-cc-mode): Set c-buffer-is-cc-mode to t.

(c-initialize-cc-mode): Set c-buffer-is-cc-mode to t.

(c-initialize-cc-mode): Require 'cc-mode-19
if functionp is not bound.  Check cc-mode-19 interface requirements.

(c-mode, c++-mode, objc-mode, java-mode, idl-mode):
Don't set comment-multi-line here.

(c-mode): c-comment-start-regexp uses
c-C++-comment-start-regexp to support line oriented comments.