Determine max_connections first, then see how large shared_buffers can

Determine max_connections first, then see how large shared_buffers can
be made, to avoid corner cases where max_connections ends up unreasonably
small because shared_buffers is hogging too much shmem space.  Per pghackers
discussion about a week ago.  Also, fix the copy-newlines problem in a
more robust way, by using COPY FROM filename instead of COPY FROM STDIN;
per a suggestion from Peter.