Decimal implementation.

This patch implements decimal support for text based formats.

Change-Id: I8e2c9e512ed149fe965216a72cb21fffd4f18e75
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1669
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: Nong Li <nong@cloudera.com>
Close all queries in test_cancellation

The queries in test_cancellation are currently cancelled but not closed, causing some test
queries to eventually time out because the admission controller limits are passed. This
patch ensures that all queries issued in test_cancellation are closed.

Change-Id: I65b26672155e31889bb6f43d3ac87be0f7b4eb72
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2187
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins
Dynamically scale down mem usage in scanners and io mgr.

This patch scales down the amount of buffering in the io mgr and the number
of scanner threads if the query is close to mem limits.

Change-Id: I68ef247a68642939b98ec7c429dfd393b23a20d2
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1906
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins