Optimize some code in the receiving side of a Motion.
Optimize some code in the receiving side of a Motion.

processIncomingChunks() receives a list of chunks from a one sender, and
then calls addChunkToSorter() on each chunk. addChunkToSorter() looks up
some things based on the sender. But since all the chunks came from the
same sender, we can move the lookups to outside of the loop and save some
overhead.

Reviewed-by: Gang Xiong <5614de4ed36375d47b39bf47c8bdae2cb0cd0d22@pivotal.io>

greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,adam8157/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,jmcatamney/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb