protocol decoder. duplicated login should be error.
fixed debug logging flag
mail store pool. `return_pool' method at mail store holder.
protocol decoder. internal state change method from unauthenticated state to authenticated state.
authentication. login and plain authentication mechanism.
fixed a typo of white space
Merge branch 'fix_typo'
login authentication mechanism is replaced to new authentication class.
user authentication challenge-response reader. plain authentication mechanism.
protocol decoder. implemented authenticate command.
authentication capability mechanism. plain authentication capability.
unit test utility for cram-md5 authentication.

pseudo time source
pseudo random string source
authentication. cram-md5 authentication mechanism.
user authentication challenge-response reader. cram-md5 authentication mechanism.
authentication capability mechanism. cram-md5 authentication capability.
Merge branch 'fix_typo' into auth

Conflicts:
	lib/rims/server.rb
hostname parameter is added to server configuration class.
changelog: * lib/rims/auth.rb, lib/rims/protocol.rb, lib/rims/server.rb, test/test_auth.rb, test/test_protocol_auth.rb, test/test_protocol_decoder.rb: implemented user authentication mechanism and added IMAP authenticate command. capable authentication types are `plain' and `cram-md5'.
Merge branch 'auth'