Use parallel scan when LIMIT with no ORDER BY
Removing unused RowCounter hierarchy and serial iterators
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/main/java/com/salesforce/phoenix/execute/ScanPlan.java
	src/main/java/com/salesforce/phoenix/iterate/SaltingSerialIterators.java
	src/test/java/com/salesforce/phoenix/end2end/QueryPlanTest.java