Fix SF bug #474538: Memory (reference) leak in poller.register (Dave Brueck)

Replace some tortuous code that was trying to be clever but forgot to
DECREF the key and value, by more longwinded but obviously correct
code.

(Inspired by but not copying the fix from SF patch #475033.)
diff --git a/Modules/selectmodule.c b/Modules/selectmodule.c
index e480fb4..348987b 100644
--- a/Modules/selectmodule.c
+++ b/Modules/selectmodule.c
@@ -366,6 +366,7 @@
 {
 	PyObject *o, *key, *value;
 	int fd, events = POLLIN | POLLPRI | POLLOUT;
+	int err;
 
 	if (!PyArg_ParseTuple(args, "O|i:register", &o, &events)) {
 		return NULL;
@@ -376,11 +377,20 @@
 
 	/* Add entry to the internal dictionary: the key is the 
 	   file descriptor, and the value is the event mask. */
-	if ( (NULL == (key = PyInt_FromLong(fd))) ||
-	     (NULL == (value = PyInt_FromLong(events))) ||
-	     (PyDict_SetItem(self->dict, key, value)) == -1) {
+	key = PyInt_FromLong(fd);
+	if (key == NULL)
+		return NULL;
+	value = PyInt_FromLong(events);
+	if (value == NULL) {
+		Py_DECREF(key);
 		return NULL;
 	}
+	err = PyDict_SetItem(self->dict, key, value);
+	Py_DECREF(key);
+	Py_DECREF(value);
+	if (err < 0)
+		return NULL;
+
 	self->ufd_uptodate = 0;
 		       
 	Py_INCREF(Py_None);