Delete trailing whitespace.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Correct error message.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Rename "args" to "mboxes", since that is what the args are
Pass arguments through from top-level

Pass the script arguments through explicitly from the top-level,
rather than relying on OptionParser.parse_args() grabbing the
arguments from sys.argv.  This makes it possible to use the file as a
module in a somewhat meaningful way.
Move an option consistency check to get_arguments()
Extract a function process(), to make it easier to use file as a module

This enables starting the culling from a short file that can be as
simple as this:

    import imapdedup

    class options:
        server = 'imap.example.com'
        port = None
        ssl = True
        user = 'me'
        password = 'Pa$$w0rd'
        verbose = False
        dry_run = False
        use_checksum = False
        use_id_in_checksum = False
        just_list = False

    mboxes = [
        'INBOX',
        'Some other mailbox',
        ]

    imapdedup.process(options, mboxes)

This, in turn, is nice because it doesn't require a password to be
passed to the program via a command-line argument, where it could be
seen by other users of the system.  (This short startup file could be
made read-only.)
Merge pull request #11 from mhagger/modulize

Make it easier to use imapdedup.py as a Python module