constify command prefix

constify command prefix

This constifies the "prefix" argument to the various command-adding
functions.

2014-07-24  Tom Tromey  <tromey@redhat.com>

	* cli/cli-decode.c (print_help_for_command): Make "prefix" const.
	(add_prefix_cmd, add_abbrev_prefix_cmd, apropos_cmd, help_list)
	(help_cmd_list): Constify.
	(lookup_cmd): Update.
	* cli/cli-decode.h (struct cmd_list_element) <prefixname>: Now
	const.
	(help_cmd_list, apropos_cmd): Update.
	* cli/cli-script.c (show_user): Update.
	* cli/cli-setshow.c (cmd_show_list): Make "prefix" const.
	* cli/cli-setshow.h (cmd_show_list): Update.
	* command.h (add_prefix_cmd, add_abbrev_prefix_cmd, help_list)
	(cmd_show_list): Update.
	* guile/scm-cmd.c (cmdscm_destroyer): Update.
	* python/py-cmd.c (cmdpy_destroyer): Update.