Added a print of the shapes of the inputs in case of an error.

doc/tutorial/extending_theano_c.txt

@@ -560,7 +560,7 @@ C code.
             return gof.Apply(self, [x, y], [output_var])
 
         def c_code_cache_version(self):
-            return (1, 0, 1)
+            return (1, 0, 2)
 
         def c_support_code(self):
             c_support_code = """
@@ -611,7 +611,10 @@ C code.
             // Validate that the inputs have the same shape
             if ( !vector_same_shape(%(x)s, %(y)s))
             {
-                PyErr_Format(PyExc_ValueError, "x.shape[0] != y.shape[0]");
+                PyErr_Format(PyExc_ValueError, "Shape mismatch : "
+                            "x.shape[0] and y.shape[0] should match but "
+                            "x.shape[0] == %%i and y.shape[0] == %%i",
+                            PyArray_DIMS(%(x)s)[0], PyArray_DIMS(%(y)s)[0]);
                 %(fail)s;
             }