Log Message:
Update to 4.6.3. From the changelog:

- fix regression introduced in 4.6.0 where atime on mbox files would
    get updated (i.e. not set back), making it difficult for other
    programs to tell if there was new mail or not without actually
    opening the mbox. Thanks: Tim van der Molen.

- fix regression: spurious errors thrown when required multidrop
    retriever parameter "envelope_recipient" not present in getmailrc
    file. Thanks: Elliot Schlegelmilch.

- fix regression: getmail_fetch no longer properly supported external
    MDAs because of problems parsing the arguments to them. Thanks: ?.

- change getmail's handling of regular expressions in the "locals"
    parameter of MultiSorter destination to allow it to handle
    backslashes correctly. Unfortunately this means complicating
    the configuration syntax slightly. Thanks: Tim van der Molen.

- update filters to use new configuration code. Remove obsolete code.