raise TypeError instead of dgpyError in dg.plug

As, from the docs:
> Passing arguments of the wrong type (e.g. passing a list when an int
> is expected) should result in a TypeError.

Thanks @jmirabel

src/dynamic_graph/dynamic-graph-py.cc

@@ -17,13 +17,7 @@ namespace python {
 /**
    \brief plug a signal into another one.
 */
-PyObject* plug(
-#if PY_MAJOR_VERSION >= 3
-    PyObject* m, PyObject* args
-#else
-    PyObject*, PyObject* args
-#endif
-    ) {
+PyObject* plug(PyObject* /*self*/, PyObject* args) {
   PyObject* objOut = NULL;
   PyObject* objIn = NULL;
   void* pObjOut;
@@ -47,21 +41,19 @@ PyObject* plug(
   pObjIn = PyCapsule_GetPointer(objIn, "dynamic_graph.Signal");
   SignalBase<int>* signalIn = (SignalBase<int>*)pObjIn;
   if (signalIn == NULL) {
-      struct module_state* st = GETSTATE(m);
       std::ostringstream oss;
       oss << "dynamic_graph.plug(a, b): Argument 'b' must be of type 'dynamic_graph.Signal', but got "
           << PyCapsule_GetName(objIn);
-      PyErr_SetString(st->dgpyError, oss.str().c_str());
+      PyErr_SetString(PyExc_TypeError, oss.str().c_str());
       return NULL;
   }
   pObjOut = PyCapsule_GetPointer(objOut, "dynamic_graph.Signal");
   SignalBase<int>* signalOut = (SignalBase<int>*)pObjOut;
   if (signalOut == NULL) {
-      struct module_state* st = GETSTATE(m);
       std::ostringstream oss;
       oss << "dynamic_graph.plug(a, b): Argument 'a' must be of type 'dynamic_graph.Signal', but got "
           << PyCapsule_GetName(objOut);
-      PyErr_SetString(st->dgpyError, oss.str().c_str());
+      PyErr_SetString(PyExc_TypeError, oss.str().c_str());
       return NULL;
   }
   std::ostringstream os;

unitTesting/test_bindings.py

@@ -20,12 +20,12 @@ class BindingsTests(unittest.TestCase):
         dg.plug(first.signal('out_double'), second.signal('in_double'))
 
         # Check that we can't connect first.out to second
-        with self.assertRaises(dg.dgpyError) as cm_in:
+        with self.assertRaises(TypeError) as cm_in:
             dg.plug(first.signal('out_double'), second)
         self.assertEqual(str(cm_in.exception), ERR % 'b')
 
         # Check that we can't connect first to second.in
-        with self.assertRaises(dg.dgpyError) as cm_out:
+        with self.assertRaises(TypeError) as cm_out:
             dg.plug(first, second.signal('in_double'))
         self.assertEqual(str(cm_out.exception), ERR % 'a')