Create a toggle between block and line comments in CC Mode.

Create a toggle between block and line comments in CC Mode.

Also (unrelated change) initialize the modes' keymaps at each loading.

* lisp/progmodes/cc-cmds.el (c-update-modeline): amend for the new information
on the modeline.
(c-block-comment-flag): New variable.
(c-toggle-comment-style): New function.

* lisp/progmodes/cc-langs.el (c-block-comment-starter)
(c-line-comment-starter): Make them c-lang-defvars.
(c-block-comment-is-default): New c-lang-defvar.
(comment-start, comment-end): Make the default values dependent on
c-block-comment-is-default.

* lisp/progmodes/cc-mode.el (c-mode-base-map): Define C-c C-k in this map.
(c-basic-common-init): Initialize c-block-comment-flag.
(c-mode-map, c++-mode-map, objc-mode-map, java-mode-map, idl-mode-map)
(pike-mode-map, awk-mode-map): Make entries in these key maps each time the
mode is loaded rather than just once per Emacs session.

* doc/misc/cc-mode.texi (Comment Commands): Introduce the notion of comment
style.
(Minor Modes): Define comment style.  Describe how comment style influences
the information displayed on the modeline.  Document c-toggle-comment-style.
(FAQ): Add a question about toggling the comment style.