[Twisted-Python] suggestions for changes to PB

[Itamar Shtull-Trauring]

Refactoring:

1) For clarity's sake, turn pb into a package:
    pb.local
    pb.remote
    pb.protocol

2) the methods for connecting to a server assume you are using TCP - they 
should use the new connectTCP, connectSSL, etc. API when we do *that* refactor.


Added functionality:

1) Use SRP instead of whatever the current challenge/response is - see 
http://www-cs-students.stanford.edu/~tjw/srp/.

2) Make a login system that uses X.509 certificates for identities (SSL only).

3) Look at SPKI for an alternate certificate-based system (RFC 2693).