Refs #9 -- Validate for mixing of types in set names.

As RFC 2622 says:
All the set name components of an hierarchical name has to be of
the same type. For example, the following names are valid:
AS1:AS-CUSTOMERS, AS1:RS-EXPORT:AS2, RS-EXCEPTIONS:RS-BOGUS

irrd/rpsl/fields.py

@@ -241,6 +241,10 @@ def clean(self, value: str, messages: RPSLParserMessages, strict_validation=True
                     f"Invalid set {value}: component {component} is not a valid AS number nor a valid set name"
                 )
                 return None
+            if strict_validation and not cleaned_as_number and not component.upper().startswith(self.prefix):
+                messages.error(f"Invalid set {value}: component {component} is not a valid AS number, "
+                               f"nor does it start with {self.prefix}")
+                return None
 
             if cleaned_as_number:
                 output_components.append(cleaned_as_number)

irrd/rpsl/tests/test_fields.py

@@ -163,6 +163,7 @@ def test_validate_set_name_field():
 
     assert_validation_err("at least one component must be an actual set name", field.clean, "AS1",)
     assert_validation_err("at least one component must be an actual set name", field.clean, "AS1:AS3")
+    assert_validation_err("not a valid AS number, nor does it start with AS-", field.clean, "AS1:AS-FOO:RS-FORBIDDEN")
     assert_validation_err("not a valid AS number nor a valid set name", field.clean, ":AS-FOO")
     assert_validation_err("not a valid AS number nor a valid set name", field.clean, "AS-FOO:")
     assert_validation_err("reserved word", field.clean, "AS1:AS-ANY")