Support python(pre|ap)pend on static methods in classic mode

Adding a test that covers this case to the python_append test-suite
Note: staticmethod function has been available since Python 2.2

Examples/test-suite/python_append.i

@@ -12,6 +12,9 @@ def grabpath():
     return funcpath
 def grabstaticpath():
     return staticfuncpath
+def clearstaticpath():
+    global staticfuncpath
+    staticfuncpath = None
 %}
 
 %pythonappend Test::func %{