server: Have the first write error cause everything to shutdown

This patch updates lockedWriter to shutdown the connection on the first
error return from Write().  This means that all the currently executing
goroutines will also get errors during their write on that socket, and
the read call will also fail, causing the main handler to terminate.

With short expected RPC latencies, we shouldn't have any goroutines
hanging around for that long after the connection fails.
server: logging++
server: clean up logging