Move interrupt checking from ExecProcNode() to executor nodes.

In a followup commit ExecProcNode(), and especially the large switch
it contains, will largely be replaced by a function pointer directly
to the correct node. The node functions will then get invoked by a
thin inline function wrapper. To avoid having to include miscadmin.h
in headers - CHECK_FOR_INTERRUPTS() - move the interrupt checks into
the individual executor routines.

While looking through all executor nodes, I noticed a number of
arguably missing interrupt checks, add these too.

Author: Andres Freund, Tom Lane
Reviewed-By: Tom Lane
Discussion:
    https://postgr.es/m/22833.1490390175@sss.pgh.pa.us

src/backend/executor/nodeSetOp.c

@@ -47,6 +47,7 @@
 #include "access/htup_details.h"
 #include "executor/executor.h"
 #include "executor/nodeSetOp.h"
+#include "miscadmin.h"
 #include "utils/memutils.h"
 
 
@@ -185,6 +186,8 @@ ExecSetOp(SetOpState *node)
 	SetOp	   *plannode = (SetOp *) node->ps.plan;
 	TupleTableSlot *resultTupleSlot = node->ps.ps_ResultTupleSlot;
 
+	CHECK_FOR_INTERRUPTS();
+
 	/*
 	 * If the previously-returned tuple needs to be returned more than once,
 	 * keep returning it.
@@ -428,6 +431,8 @@ setop_retrieve_hash_table(SetOpState *setopstate)
 	 */
 	while (!setopstate->setop_done)
 	{
+		CHECK_FOR_INTERRUPTS();
+
 		/*
 		 * Find the next entry in the hash table
 		 */