Python 3 C API changes

These changes make the C/Python API files compile under both Python 2 and 3. Under Python 2 all tests pass (for all of tdaq-common), so I would say it is safe to put this into nightly. There was nothing done to port the actual Python code to version 3 yet, so many of the tests don't get very far. But this can be done in a separate step.

The following tests FAILED:
          1 - PyTest (Failed)
         17 - mkfile (Failed)
         18 - py (Failed)
         19 - bench_data_read (Child aborted)
         20 - bench_header_access (Failed)
         21 - bench_validate (Child aborted)
         23 - bench_streamtag (Failed)
         24 - rmfile (Failed)

eformat/python/container.h

@@ -157,13 +157,13 @@ namespace eformat { namespace python {
             || PyTuple_Check(obj_ptr)
             || PyIter_Check(obj_ptr)
             || PyRange_Check(obj_ptr)
-            || (   !PyString_Check(obj_ptr)
-                && !PyUnicode_Check(obj_ptr)
+            || (!PyUnicode_Check(obj_ptr)
+                && !PyBytes_Check(obj_ptr)
                 && (   obj_ptr->ob_type == 0
-                    || obj_ptr->ob_type->ob_type == 0
-                    || obj_ptr->ob_type->ob_type->tp_name == 0
+                    || obj_ptr->ob_type->tp_base == 0
+                    || obj_ptr->ob_type->tp_base->tp_name == 0
                     || std::strcmp(
-                         obj_ptr->ob_type->ob_type->tp_name,
+                         obj_ptr->ob_type->tp_base->tp_name,
                          "Boost.Python.class") != 0)
                 && PyObject_HasAttrString(obj_ptr, "__len__")
                 && PyObject_HasAttrString(obj_ptr, "__getitem__")))) return 0;