Log Message:
bftpd: Update to 5.1

Jesse Smith <jessefrgsmith@yahoo.ca> -> 5.1
        - Fixed duplicate error message when user tries to
          sign in with invalid username.
        - Make sure user can change username before
          successfully authenticating.
        - Fix error message when "type" command is not
          given a parameter.
        - Make sure we do not return multiple error
          codes when an account is disabled.
        - Do not drop connection to client when
          selected account is disabled.
        - Make sure when accounts are disabled/denied, they print the
          proper reason (set in the config file) back to the client