IMPALA-1441: Wrong results with outer joins in inline views

This commit fixes the issue where additional predicates that alter the
meaning of a query are generated when an inline view contains an outer
join. Such predicates are derived from slot equivalences withouth taking
into account the directionality of the value transfer graph.

Change-Id: I0a3390d39a4f2039a8b114a7659980aa444d35c0
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5109
Reviewed-by: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Tested-by: jenkins