Add max / min_*int() builtins

It would have been convenient today to know the largest values that
Impala accepts for its integer types. This patch adds max and min
builtins for our numeric types.

[localhost:21000] > select max_bigint(), max_int(), max_smallint(),
max_tinyint();
Query: select max_bigint(), max_int(), max_smallint(), max_tinyint()
+---------------------+------------+----------------+---------------+
| max_bigint()        | max_int()  | max_smallint() | max_tinyint() |
+---------------------+------------+----------------+---------------+
| 9223372036854775807 | 2147483647 | 32767          | 127           |
+---------------------+------------+----------------+---------------+

Change-Id: I6df6df2728197529c6375dbb1b7d3c9ddb9833d2
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2381
Reviewed-by: Henry Robinson <henry@cloudera.com>
Tested-by: jenkins