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/nodeHash.c

@@ -810,6 +810,9 @@ ExecHashIncreaseNumBuckets(HashJoinTable hashtable)
 			idx += MAXALIGN(HJTUPLE_OVERHEAD +
 							HJTUPLE_MINTUPLE(hashTuple)->t_len);
 		}
+
+		/* allow this loop to be cancellable */
+		CHECK_FOR_INTERRUPTS();
 	}
 }
 
@@ -1192,6 +1195,9 @@ ExecScanHashTableForUnmatched(HashJoinState *hjstate, ExprContext *econtext)
 
 			hashTuple = hashTuple->next;
 		}
+
+		/* allow this loop to be cancellable */
+		CHECK_FOR_INTERRUPTS();
 	}
 
 	/*