control_send: use separate buffer for reading from stream
control_send: use separate buffer for reading from stream

On certain error messages we print what we read from the stream, which
is garbage if we are writing at that same buffer.  Reported by Niels.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb