Fix list:true when referencing a cached schema

[pd]

When using the list: true option, if the schema has already been cached in Validator.schemas, json-schema would not wrap the schema in { "type": "array", "items": ... } as expected.

Test included to demonstrate the failure; the fix was to use fake_uri as is done elsewhere to generate an identifier for the wrapper schema. I didn't add a test to the test_jsonschema_draft3 file, as this appears to be an identical code path, so the duplication shouldn't be necessary AFAICT.

[hoxworth]

Thanks @pd . Moved the test to a separate 'test_list_option.rb' test file, as it isn't really a draft-04 test, but this is great. Released as 2.2.4.