Use ctl-x-map in place of C-x (bug#10566)

Use ctl-x-map in place of C-x (bug#10566)

For an example of the problems NOT doing this might cause, see eg
http://lists.gnu.org/archive/html/bug-gnu-emacs/2006-07/msg00000.html
Eg after:
  (global-set-key (kbd "C-u") ctl-x-map)
  (global-set-key (kbd "C-x") 'universal-argument)
just loading dired-x.el or term.el would give an error.

* lisp/dired-x.el (dired-bind-jump): Use ctl-x-map and ctl-x-4-map.
* lisp/term.el (term-raw-escape-map): Use Control-X-prefix.
* lisp/vc/vc-hooks.el (vc-prefix-map): Use ctl-x-map.