improvements to userlist inc. unprivileged mode

Replaced double verbose mode with -g
(double verbose mode now reserved for processing rest of gecos data)

Colour options are now c and C.

Added oneline mode (-o) with -w to force it off.

-g Shows group info.

Newlines are now at the start of successive printf() format strings.
And show_groups* prints the final newline.

Replaced "locked-B" with "LOCKED".

Renamed process_user_list() to process_users_full() and added
process_users_minimal().

All variables are in lower case.

Removed duplicate "\!*) pwstatus=locked ;;" line.

Added sanity checking section
With check for an unprivileged user forgetting the -u option.

Added the following format string fragment variables (some of which are
defined differently depending on whether oneline mode is active):
  passwd_header_format
  passwd_field_format
  username_header_format
  username_field_format
  status_field_format