The previous commit introduced a new interface for the auth modules. This
commit simply updates the other auth modules to use the new interface.
The basic auth module is also updated so that if a user has a shadow
password entry indicated, but the shadow entry cannot be found, an error
is logged rather than silently succeeding.
The BSD authentication module is also updated to allow it to be
compiled on a Linux system for basic testing.
The loadable sesman authentication modules use different types for the
authentication handle returned from auth_userpass(). The PAM module
uses a pointer, and the other modules use (effectively) a boolean. Within
sesman itself, a long or tbus (intptr_t) is used.
This PR replaces all of these types with a pointer to an incomplete type.
Consequently:-
- A single better-labelled type is used it all places within sesman so
it's more obvious what's being handled.
- There is no need to cast the authentication handle within the PAM
module to a long and back again.
- The compiler can check function signatures between auth.h and the
various verify modules.
Include string.h for strcmp(). Don't define _XOPEN_SOURCE, it conflicts
with libc headers and hides putpwent(). Make input strings constant. Fix
functions to match their declarations.
