Backport minidom attribute tests from default (73c76466cf44).

Some minidom code changed between 3.2 and 3.3, so to be sure to avoid
differenced in behavior I’m backporting these tests added by MvL.
diff --git a/Lib/test/test_minidom.py b/Lib/test/test_minidom.py
index f3fa1b8..4a69b00 100644
--- a/Lib/test/test_minidom.py
+++ b/Lib/test/test_minidom.py
@@ -350,13 +350,31 @@
     def testGetAttrList(self):
         pass
 
-    def testGetAttrValues(self): pass
+    def testGetAttrValues(self):
+        pass
 
-    def testGetAttrLength(self): pass
+    def testGetAttrLength(self):
+        pass
 
-    def testGetAttribute(self): pass
+    def testGetAttribute(self):
+        dom = Document()
+        child = dom.appendChild(
+            dom.createElementNS("http://www.python.org", "python:abc"))
+        self.assertEqual(child.getAttribute('missing'), '')
 
-    def testGetAttributeNS(self): pass
+    def testGetAttributeNS(self):
+        dom = Document()
+        child = dom.appendChild(
+                dom.createElementNS("http://www.python.org", "python:abc"))
+        child.setAttributeNS("http://www.w3.org", "xmlns:python",
+                                                "http://www.python.org")
+        self.assertEqual(child.getAttributeNS("http://www.w3.org", "python"),
+            'http://www.python.org')
+        self.assertEqual(child.getAttributeNS("http://www.w3.org", "other"),
+            '')
+        child2 = child.appendChild(dom.createElement('abc'))
+        self.assertEqual(child2.getAttributeNS("http://www.python.org", "missing"),
+                         '')
 
     def testGetAttributeNode(self): pass