Add some more numeric test coverage

max(numeric) wasn't tested at all, min(numeric) was only used by some
unrelated tests.  Add explicit tests with the other numeric aggregate
functions.

src/test/regress/expected/numeric.out

@@ -1096,6 +1096,18 @@ SELECT AVG(val) FROM num_data;
  -13430913.592242320700
 (1 row)
 
+SELECT MAX(val) FROM num_data;
+        max         
+--------------------
+ 7799461.4119000000
+(1 row)
+
+SELECT MIN(val) FROM num_data;
+         min          
+----------------------
+ -83028485.0000000000
+(1 row)
+
 SELECT STDDEV(val) FROM num_data;
             stddev             
 -------------------------------

src/test/regress/sql/numeric.sql

@@ -752,6 +752,8 @@ SELECT power('-inf'::numeric, '-inf');
 -- ******************************
 -- numeric AVG used to fail on some platforms
 SELECT AVG(val) FROM num_data;
+SELECT MAX(val) FROM num_data;
+SELECT MIN(val) FROM num_data;
 SELECT STDDEV(val) FROM num_data;
 SELECT VARIANCE(val) FROM num_data;