COPY TO piped into a slower stream can freeze the pool #136

porsager#499 (COPY TO piped into createGzip(), then the pool freezes) and porsager#917 (a COPY TO readable in pipeline() sometimes never gets close) look like the paused-socket bug fixed in #69 for 4.5.0: the driver paused the socket for backpressure and never resumed it when the COPY ended. Not claimed until a test runs each reporter's scenario against real PostgreSQL, fails on 3.4.9 and passes here.