Improve compilation errors for 'consume' and cypclass aliasing

Cython/Compiler/ExprNodes.py

@@ -11375,7 +11375,7 @@ class ConsumeNode(ExprNode):
         self.operand = self.operand.analyse_types(env)
         operand_type = self.operand.type
         if not operand_type.is_cyp_class:
-            error(self.pos, "Can only consume cypclass")
+            error(self.pos, "Can only consume cypclass (not '%s')" % operand_type)
             self.type = PyrexTypes.error_type
             return self
         if operand_type.is_qualified_cyp_class:

Cython/Compiler/PyrexTypes.py

@@ -4894,6 +4894,8 @@ class QualifiedCypclassType(BaseType):
         return self.assignable_from_resolved_type(src_type.resolve())
 
     def assignable_from_resolved_type(self, src_type):
+        if src_type is error_type:
+            return 1
         if src_type.is_null_ptr:
             return 1
         if src_type.is_qualified_cyp_class and src_type.qualifier in self.assignable_to[self.qualifier]: