SQL Editor hangs on COPY TO STDOUT

If you run something like:

copy (select * from pg_stat_activity) to stdout;

in the query editor, it will hang forever. The code in
pgQueryThread::execute() doesn't check for a PGRES_COPY_OUT result, and
calls PQgetResult() repeatedly. PQgetResult() will keep on returning
PGRES_COPY_OUT until the copy output is read with PQgetCopyData(), so it
gets stuck. COPY FROM STDOUT has a similar problem.

Attached is a patch to fix that. For COPY TO STDOUT, it prints the first
100 rows to the message display. For COPY FROM STDIN, it throws an error.

- Heikki