[fix] Check for errors in PyArray_CanCastTypeto DEPRECATE

If a user had set warnings to raise errors, then this DEPRECATE would
leave us with an unpropagated exception and cause havoc downstream.

Unfortunately there is no way to propagate an exception from here, so
we just have to throw it away :-(. But this is still better than the
alternative...

Conflicts:
	numpy/core/tests/test_ufunc.py

numpy/core/src/multiarray/convert_datatype.c

@@ -564,9 +564,13 @@ PyArray_CanCastTypeTo(PyArray_Descr *from, PyArray_Descr *to,
         same_kind_ok = PyArray_CanCastTypeTo_impl(from, to,
                                                   NPY_SAME_KIND_CASTING);
         if (unsafe_ok && !same_kind_ok) {
-            DEPRECATE("Implicitly casting between incompatible kinds. In "
-                      "a future numpy release, this will raise an error. "
-                      "Use casting=\"unsafe\" if this is intentional.");
+            if (DEPRECATE("Implicitly casting between incompatible kinds. In "
+                          "a future numpy release, this will raise an error. "
+                          "Use casting=\"unsafe\" if this is intentional.")
+                < 0) {
+                /* We have no way to propagate an exception :-( */
+                PyErr_Clear();
+            }
         }
         return unsafe_ok;
     }