* cli/cli-decode.c (add_alias_cmd): Make a copy of doc field
if flags contains DOC_ALLOCATED.
(add_setshow_cmd_full): Add DOC_ALLOCATED to set and show
flags.
(delete_cmd): Handle DOC_ALLOCATED flag.
* cli/cli-decode.h (DOC_ALLOCATED): New macro for use
in flags filed of struct cmd_list_element.
(struct cmd_list_element): Document new flag item.