Nested references are not resolved for local files

If #454 testcases are changed to use a relative file reference, the nested definitions are not resolved.

tags:
- name: admins
  description: Secured Admin-only calls
- name: developers
  description: Operations available to regular developers
paths:
  /inventory:
    get:
      summary: searches inventory test
      operationId: searchInventory
      responses:
        200:
          description: search results matching criteria
        default:
          $ref: './issue-454-file-components.yaml#/responses/GeneralError'
definitions:
  ModelWithNestedProperties:
    properties:
      remoteProperty:
        $ref: './issue-454-file-components.yaml#/definitions/RemoteComponent'

Test case:

    @Test
    public void testNestedFileRefs() {
        Swagger swagger = new SwaggerParser().read("src/test/resources/nested-file-references/issue-454-file.yaml",
                null, true);

        assertNotNull(swagger.getDefinitions().get("ErrorModel"));
        assertNotNull(swagger.getDefinitions().get("ModelWithNestedProperties"));

        ModelImpl model = (ModelImpl)swagger.getDefinitions().get("ModelWithNestedProperties");
        Property property = model.getProperties().get("remoteProperty");
        assertNotNull(property);
        assertTrue(property instanceof RefProperty);
        RefProperty ref = (RefProperty) property;
        assertEquals(ref.get$ref(), "#/definitions/RemoteComponent");
        assertNotNull(swagger.getDefinitions().get("NestedProperty"));

        ModelImpl nestedModel = (ModelImpl)swagger.getDefinitions().get("NestedProperty");
        assertNotNull(nestedModel);
        assertNotNull(nestedModel.getProperties().get("name"));
        assertTrue(nestedModel.getProperties().get("name") instanceof StringProperty);
    }

The attached tar ball contains a testcase and test data to reproduce the issue.
test.tar.gz

Start with the nested-file-references/issue-454-file.yaml fixture and run SwaggerParser.read as shown in testNestedFileRefs. Compare the resolved definitions and remoteProperty reference with the assertions in the test; done means the nested references resolve and all listed assertions pass.