Updated cv2.cpp to support Python 3 API.

Added a header with defines to enable the module to compile with either
python 2 or 3 without changes.

modules/python/src2/cv2.cpp

@@ -23,6 +23,8 @@
 #  include "opencv2/nonfree.hpp"
 #endif
 
+#include "pycompat.hpp"
+
 using cv::flann::IndexParams;
 using cv::flann::SearchParams;
 
@@ -1176,7 +1178,11 @@ static int convert_to_char(PyObject *o, char *dst, const char *name = "no_name")
   }
 }
 
+#if PY_MAJOR_VERSION >= 3
+#define MKTYPE2(NAME) pyopencv_##NAME##_specials(); if (!to_ok(&pyopencv_##NAME##_Type)) return NULL;
+#else
 #define MKTYPE2(NAME) pyopencv_##NAME##_specials(); if (!to_ok(&pyopencv_##NAME##_Type)) return
+#endif
 
 #ifdef __GNUC__
 #  pragma GCC diagnostic ignored "-Wunused-parameter"
@@ -1205,15 +1211,35 @@ static int to_ok(PyTypeObject *to)
   return (PyType_Ready(to) == 0);
 }
 
+
+#if PY_MAJOR_VERSION >= 3
+extern "C" CV_EXPORTS PyObject* PyInit_cv2();
+static struct PyModuleDef cv2_moduledef =
+{
+    PyModuleDef_HEAD_INIT,
+    MODULESTR,
+    "Python wrapper for OpenCV.",
+    -1,     /* size of per-interpreter state of the module,
+               or -1 if the module keeps state in global variables. */
+    methods
+};
+
+PyObject* PyInit_cv2()
+#else
 extern "C" CV_EXPORTS void initcv2();
 
 void initcv2()
+#endif
 {
   import_array();
 
 #include "pyopencv_generated_type_reg.h"
 
+#if PY_MAJOR_VERSION >= 3
+  PyObject* m = PyModule_Create(&cv2_moduledef);
+#else
   PyObject* m = Py_InitModule(MODULESTR, methods);
+#endif
   PyObject* d = PyModule_GetDict(m);
 
   PyDict_SetItemString(d, "__version__", PyString_FromString(CV_VERSION));
@@ -1262,5 +1288,7 @@ void initcv2()
   PUBLISH(CV_64FC4);
 
 #include "pyopencv_generated_const_reg.h"
-
+#if PY_MAJOR_VERSION >= 3
+    return m;
+#endif
 }