python: also catch general c++ exceptions

they might be thrown from third-party code (notably Ogre in the ovis
module).
While Linux is kind enough to print them, they cause instant termination
on Windows.
Arguably, they do not origin from OpenCV itself, but still this helps
understanding what went wrong when calling an OpenCV function.

modules/python/test/test_misc.py

@@ -47,6 +47,12 @@ class Bindings(NewOpenCVTests):
         boost.getMaxDepth()  # from ml::DTrees
         boost.isClassifier()  # from ml::StatModel
 
+    def test_raiseGeneralException(self):
+        with self.assertRaises((cv.error,),
+                            msg='C++ exception is not propagated to Python in the right way') as cm:
+            cv.utils.testRaiseGeneralException()
+        self.assertEqual(str(cm.exception), 'exception text')
+
     def test_redirectError(self):
         try:
             cv.imshow("", None)  # This causes an assert