Fix failure to account for memory used by tuplestore_putvalues().

This oversight could result in a tuplestore using much more than the
intended amount of memory.  It would only happen in a code path that loaded
a tuplestore via tuplestore_putvalues(), and many of those won't emit huge
amounts of data; but cases such as holdable cursors and plpgsql's RETURN
NEXT command could have the problem.  The fix ensures that the tuplestore
will switch to write-to-disk mode when it overruns work_mem.

The potential overrun was finite, because we would still count the space
used by the tuple pointer array, so the tuplestore code would eventually
flip into write-to-disk mode anyway.  When storing wide tuples we would
go far past the expected work_mem usage before that happened; but this
may account for the lack of prior reports.

Back-patch to 8.4, where tuplestore_putvalues was introduced.

Per bug #6061 from Yann Delorme.

src/backend/utils/sort/tuplestore.c

@@ -570,7 +570,8 @@ tuplestore_puttuple(Tuplestorestate *state, HeapTuple tuple)
 	MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
 
 	/*
-	 * Copy the tuple.	(Must do this even in WRITEFILE case.)
+	 * Copy the tuple.  (Must do this even in WRITEFILE case.  Note that
+	 * COPYTUP includes USEMEM, so we needn't do that here.)
 	 */
 	tuple = COPYTUP(state, tuple);
 
@@ -580,9 +581,8 @@ tuplestore_puttuple(Tuplestorestate *state, HeapTuple tuple)
 }
 
 /*
- * Similar to tuplestore_puttuple(), but start from the values + nulls
- * array. This avoids requiring that the caller construct a HeapTuple,
- * saving a copy.
+ * Similar to tuplestore_puttuple(), but work from values + nulls arrays.
+ * This avoids an extra tuple-construction operation.
  */
 void
 tuplestore_putvalues(Tuplestorestate *state, TupleDesc tdesc,
@@ -592,6 +592,7 @@ tuplestore_putvalues(Tuplestorestate *state, TupleDesc tdesc,
 	MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
 
 	tuple = heap_form_minimal_tuple(tdesc, values, isnull);
+	USEMEM(state, GetMemoryChunkSpace(tuple));
 
 	tuplestore_puttuple_common(state, (void *) tuple);