AuthProxy support for barcode-based login

If a user attempts to log in the catalog with a barcode, any AuthProxy authenticators, except the "native" authenticator will fail, the assumption being that the remote authenticator knows nothing about barcodes. This isn't normally a problem, as logging in with remote credentials (e.g. LDAP) usually implies logging in with your username. This does become a problem, however, when usernames and barcodes are identical in a system (say, by policy) and the usernames start with a number, which is the default "i am a barcode" regex for TPAC/JSPAC. In this case, the catalog always attempts a barcode login and AuthProxy always ignores the remote authenticators.

Incidentally, if username == barcode, using a barcode regex will obviously not suffice to differentiate between the two.

My proposal: When a barcode-based login is attempted in open-ils.auth_proxy.login, grab the username from the database matching the barcode and use that instead for all AuthProxy-based logins. Since the login dance within AuthProxy is wholly self-contained, the user ultimately receives an authentication token or a failure event. In either case, the method used within AuthProxy to attempt the login should not concern the caller.