Fix for own recent reference count error.

- The armature weakref list was  being incref'd twice then decrefed twice (incref and decref were used incorrectly), now only once. My 'fix' broke this.
- In bpy_pydriver_create_dict the 2 refs added from running PyDict_SetItemString twice were undone when clearing the dictionary (added comment)
- changed Py_XDECREF to Py_DECREF int BPY_pyconstraint_update and BPY_pyconstraint_target, Py_XDECREF checs for NULL value which would have crashed blender before it got to Py_XDECREF anyway.
- after every error is reported (PyErr_Print), remove sys.last_traceback and clear the error, I found this fixed certain crashes (usually when starting the game engine or exiting blender), so best do this all the time.

- header_text.c, CcdPhysicsEnvironment.cpp, KX_CameraActuator.cpp - remove some warnings.

source/blender/python/api2_2x/Draw.c

@@ -614,6 +614,9 @@ static void exit_pydraw( SpaceScript * sc, short err )
 
 	if( err ) {
 		PyErr_Print(  );
+		PyErr_Clear(  );
+		PySys_SetObject("last_traceback", NULL);
+		
 		script->flags = 0;	/* mark script struct for deletion */
 		SCRIPT_SET_NULL(script);
 		script->scriptname[0] = '\0';
@@ -838,6 +841,8 @@ static void exec_but_callback(void *pyobj, void *data)
 	if (!result) {
 		Py_DECREF(pyvalue);
 		PyErr_Print(  );
+		PyErr_Clear(  );
+		PySys_SetObject("last_traceback", NULL);
 		error_pyscript(  );
 	}
 	Py_XDECREF( result );
@@ -1129,6 +1134,8 @@ static PyObject *Method_UIBlock( PyObject * self, PyObject * args )
 	
 	if (!result) {
 		PyErr_Print(  );
+		PyErr_Clear(  );
+		PySys_SetObject("last_traceback", NULL);
 		error_pyscript(  );
 	} else {
 		/* copied from do_clever_numbuts in toolbox.c */

source/blender/python/api2_2x/bpy_internal_import.c

@@ -84,6 +84,8 @@ PyObject *importText( char *name )
 
 		if( PyErr_Occurred(  ) ) {
 			PyErr_Print(  );
+			PyErr_Clear(  );
+			PySys_SetObject("last_traceback", NULL);
 			free_compiled_text( text );
 			return NULL;
 		}
@@ -138,6 +140,8 @@ PyObject *reimportText( PyObject *module )
 	/* if compile failed.... return this error */
 	if( PyErr_Occurred(  ) ) {
 		PyErr_Print(  );
+		PyErr_Clear(  );
+		PySys_SetObject("last_traceback", NULL);
 		free_compiled_text( text );
 		return NULL;
 	}
@@ -182,7 +186,7 @@ static PyObject *blender_import( PyObject * self, PyObject * args,  PyObject * k
 		Py_XDECREF( exception );
 		Py_XDECREF( err );
 		Py_XDECREF( tb );
-		printf( "imported from text buffer...\n" );
+		/* printf( "imported from text buffer...\n" ); */
 	} else {
 		PyErr_Restore( exception, err, tb );
 	}