[PATCH] SIGPIPE redux -- please review

I think the patch introduces a descriptor leak. The lstream needs to be closed, but we either must avoid flushing its buffers them or ignore the SIGPIPE when we flush them. The latter will do for now, but we should add a "no flush" flag to lstreams so that the lstream close method can avoid trouble when we know the remote endpoint of a socket has gone away. Alternately an Lstream_discard_buffers function might work as well and have other uses. I'm pretty sure that I fixed the Gnus SIGPIPE crashes last year, but it probably got undone with process.c got ripped apart during the Windows frenzy. That would explain the deja vu feeling related to these crashes.