Gave the base login code the ability to find username/password from a

Gave the base login code the ability to find username/password from a
cookie.  for security reasons, we don't put login data into cookies, but if the
login info is available to us in that format already (say, via external means), we'll
use it.  This can be useful for persistent logins (e.g. self-check) or
automatic logins (pushing cookie data out to workstations)

Minor cleanup of the login code to make it more re-use friendly.

Added self-check support for verifying the staff login before each patron
login.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@17176 dcc99617-32d9-48b4-a31d-7c20da2025e4