Add a new EState member es_leaf_result_relations, so that the trigger
code knows about ResultRelInfos created by tuple routing.  Also make
sure ExplainPrintTriggers knows about partition-related
ResultRelInfos.

Etsuro Fujita, reviewed by Amit Langote

Discussion: http://postgr.es/m/57163e18-8e56-da83-337a-22f2c0008051@lab.ntt.co.jp