[hypermail] eliminating need to choose increment = 0 or 1

 The need to specify an incremental or non-incremental mode has been confusing some people, and since hypermail usually has enough info to tell which is appropriate, it seems unwise to require new users to figure this choice out.
 Also, I sometimes get annoyed when I forget to put a "-m" before an mbox name on the command line and it hangs waiting for stdin. It seems natural to attach a new meaning to files specified as command line arguments (am I correct in assuming that names not preceded by an option specifier have never meant anything to hypermail?)  If there is some demand for using an explicit option to ask hypermail to determine the update mode, I would propose "increment = -1".

 We probably shouldn't change the behavior of any existing installation, but should make new installations default to using this new mode.  I am uncertain what is the best way to control when this new mode should be active. Here are three possibilities that come to mind:

1. Any command line arguments that aren't part of an option are treated as mboxes to add to or update the archive. This is the simplest approach, but has slightly higher risk of breaking existing installations that have extraneous info on the command line.
2. Activate the new mode only when the .hmrc has some new options values which will become the default in the sample .hmrc's, probably: increment = -1 mbox =
3. Activate the new mode only when isatty(fileno(stdin)) and the current rules say it should read mail from stdin.

 Any comments?

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