(recvline): Rewrite the loop to receive a line from a socket. The new

(recvline): Rewrite the loop to receive a line from a socket.  The new
version silently truncates long lines.  The old one split them up and
got quite confused.  It got also confused when the line didn't arrive
in one piece.  Icing on the cake: it wrote beyond the end of the
buffer.  The new version is less efficient, but that doesn't matter
here.