Also merge Doxygen comments for overloaded constructors in Python.

This was done for plain functions/methods but not constructors, which don't
have "kind=function" attribute.

Just don't check for "kind" at all, the presence of "sym:overloaded" should be
good enough to indicate that it's an overloaded something.

Also add a test for overloaded constructors documentation.

Source/DoxygenTranslator/src/PyDocConverter.cpp

@@ -781,7 +781,7 @@ String *PyDocConverter::makeDocumentation(Node *n)
   currentNode = n;
 
   // for overloaded functions we must concat documentation for underlying overloads
-  if (Checkattr(n, "kind", "function") && Getattr(n, "sym:overloaded")) {
+  if (Getattr(n, "sym:overloaded")) {
     // rewind to the first overload
     while (Getattr(n, "sym:previousSibling"))
       n = Getattr(n, "sym:previousSibling");