should we keep the -1 option?

[Graham Percival <gperciva@tarsnap.com>]

In git commit 49470ac38, on 2016-02-08, we added a -1 option to spiped, which
causes the server to quit after one connection stops.  This was added to
simplify our test suite.  However, thanks to Tim Düsterhus's "Perform a
graceful shutdown on SIGTERM" (git commit 8f22fea04, on 2016-05-08), we no
longer use -1 in the test suite.

-1 has never appeared in an official spiped release, and we're considering
removing it.  Would anybody prefer it to remain?

Cheers,
- Graham Percival