#37 prevent resubmit already posted loginfor

[Giancarlo Pinerolo]

This patches to loginform.ihtml and the validatelogin
in locval.inc prevent tte resubmission of a form
already submitted, thus prevents going back with the
browser back button and repost auth credentials when
authentication is expired

[Giancarlo Pinerolo]

local.inc with extra check in auth_validatelogin

[Giancarlo Pinerolo]

loginform.ihtml that adds an uniqid hidden fiels

[Giancarlo Pinerolo]

Logged In: YES
user_id=163488

my previous version of local.inc stored the used_formidsa in
tha auth->auth persistent array.
But once someone logged off, that would be cleared, thus
again allowing going 'back' to the posted loginform

This version stores the used_formids as a persistent session
variable ($sess-Zregister("used_formids"), so oit should be
there as long the sessions is tha same.

[Giancarlo Pinerolo]

validatelogin registers and checks used_formids