Consistent error messages

Noticed that some error messages in Authlogic have a full stop while others don't. Considering that most don't, and that Rails error messages also don't include a full stop at the end of the sentence, I thought removing the full stop would probably be the best thing to do.

Updated documentation relating to these error messages. In particular the documentation for the consecutive_failed_logins_limit_exceeded error message key did not seem to fully reflect the actual code.