IMPALA-1111: Fix alignment in ReservoirSample aggregate functions

Change-Id: Iac7aa96eb19079715a7e8152a5edfeafa0d50bc7
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4478
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins
Minor PA/PHJ improvements.

- PHJ: estimate the hash table size when constructing the hash table.
- PA/PHJ: process spilled partitions in depth first order.

Change-Id: I25df6019246f9f751e376afa405bdacc79da6381
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4490
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins
Allow UDA intermediates to use CHAR. Update stddev/var to use it.

Change-Id: I791c6389978f4994cba33f01273e94343a163916
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4368
Reviewed-by: Skye Wanderman-Milne <skye@cloudera.com>
Tested-by: jenkins
IMPALA-1264: Re-enable test_session_experation.py

This has only failed once as far as I can tell, and we don't have any log
files for the failure.  Nor have I been able to repro.  So, let's increase the
test timeout to get a bit more slop in the case of the occasional long sleep
on the impalad side.  If there is a bug where a session is stuck in the
checked-out state, the test will still find it.

Change-Id: Ib63a8a83d9c3e772787dc548473868c58f950eb8
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4494
Reviewed-by: Daniel Hecht <dhecht@cloudera.com>
Tested-by: jenkins