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/nodeBitmapHeapscan.c

@@ -41,6 +41,7 @@
 #include "access/transam.h"
 #include "executor/execdebug.h"
 #include "executor/nodeBitmapHeapscan.h"
+#include "miscadmin.h"
 #include "pgstat.h"
 #include "storage/bufmgr.h"
 #include "storage/predicate.h"
@@ -192,6 +193,8 @@ BitmapHeapNext(BitmapHeapScanState *node)
 		Page		dp;
 		ItemId		lp;
 
+		CHECK_FOR_INTERRUPTS();
+
 		/*
 		 * Get next page of results if needed
 		 */