psql: Show all query results by default

psql: Show all query results by default

Previously, psql printed only the last result if a command string
returned multiple result sets.  Now it prints all of them.  The
previous behavior can be obtained by setting the psql variable
SHOW_ALL_RESULTS to off.

Author: Fabien COELHO 
Reviewed-by: "Iwata, Aya" 
Reviewed-by: Daniel Verite 
Reviewed-by: Peter Eisentraut 
Reviewed-by: Kyotaro Horiguchi 
Reviewed-by: vignesh C 
Discussion: https://www.postgresql.org/message-id/flat/alpine.DEB.2.21.1904132231510.8961@lancre