[Python] Fix docstrings for %callback functions

Reinstates autodoc for callback function testcase from #467, actually
tests the resulting docstring in the _runme.py and fixes SWIG/Python
so the expected result is obtained.

CHANGES.current

@@ -5,6 +5,9 @@ See the RELEASENOTES file for a summary of changes in each release.
 Version 3.0.8 (in progress)
 ===========================
 
+2015-09-04: olly
+	    [Python] Fix docstrings for %callback functions.
+
 2015-08-07: talby
             [Perl] tidy -Wtautological-constant-out-of-range-compare warnings when building generated code under clang
 

Examples/test-suite/autodoc.i

@@ -114,6 +114,12 @@
   }
 %}
 
+%callback("%(uppercase)s_CALLBACK") func_cb;
+
+%inline {
+  int func_cb(int c, int d) { return c; }
+}
+
 // Bug 3310528
 %feature("autodoc","1") banana; // names + types
 %inline %{

Examples/test-suite/python/autodoc_runme.py

@@ -355,4 +355,5 @@ check(funkdefaults.__doc__,
 check(func_input.__doc__, "func_input(int * INPUT) -> int")
 check(func_output.__doc__, "func_output() -> int")
 check(func_inout.__doc__, "func_inout(int * INOUT) -> int")
+check(func_cb.__doc__, "func_cb(int c, int d) -> int")
 check(banana.__doc__, "banana(S a, S b, int c, Integer d)")

Source/Modules/python.cxx

@@ -2389,7 +2389,7 @@ public:
       Printv(f_dest, tab4 "return ", funcCall(name, callParms), "\n", NIL);
     }
 
-    if (Getattr(n, "feature:python:callback") || !have_addtofunc(n)) {
+    if ((Getattr(n, "feature:python:callback") && !have_docstring(n)) || !have_addtofunc(n)) {
       /* If there is no addtofunc directive then just assign from the extension module (for speed up) */
       Printv(f_dest, name, " = ", module, ".", name, "\n", NIL);
     }