Fix pgbench's parsing of double values to notice trailing garbage.

Noted by Fabien Coelho, though this isn't exactly his proposed patch.
(The technique used here is borrowed from the zic sources.)

src/bin/pgbench/pgbench.c

@@ -928,8 +928,9 @@ makeVariableNumeric(Variable *var)
 	else /* type should be double */
 	{
 		double dv;
+		char xs;
 
-		if (sscanf(var->value, "%lf", &dv) != 1)
+		if (sscanf(var->value, "%lf%c", &dv, &xs) != 1)
 		{
 			fprintf(stderr,
 					"malformed variable \"%s\" value: \"%s\"\n",