Add link to Ubuntu bug about disabling database and user completions.

contrib/postgresql

@@ -6,7 +6,7 @@
 have psql && {
 _pg_databases()
 {
-	return # intentionally disabled in 7ebed6af (TODO: why?)
+	return # See https://launchpad.net/bugs/164772
 	COMPREPLY=( $( compgen -W "$( psql -l 2>/dev/null | \
 			sed -e '1,/^-/d' -e '/^(/,$d' | \
 			awk '{print $1}' )" -- $cur ) )
@@ -14,6 +14,7 @@ _pg_databases()
 
 _pg_users()
 {
+	# See https://launchpad.net/bugs/164772
 	#COMPREPLY=( $( psql -qtc 'select usename from pg_user' template1 2>/dev/null | \
 	#		grep "^ $cur" ) )
 	#[ ${#COMPREPLY[@]} -eq 0 ] && COMPREPLY=( $( compgen -u -- $cur ) )