(Re-)enable more doctests.

It is way too easy to silently pass these :( -- specifically,
the doctest directive only works for things with >>> prompts.

Author: Julian

docs/faq.rst

@@ -150,7 +150,7 @@ this code, we add the default properties to each object *before* the
 properties are validated, so the default values themselves will need to
 be valid under the schema.)
 
-    .. code-block:: python
+    .. testcode::
 
         from jsonschema import Draft7Validator, validators
 
@@ -205,7 +205,7 @@ defaults.
     all of its properties, but only if your schema provides a default
     value for the object itself, like so:
 
-    .. code-block:: python
+    .. testcode::
 
         schema = {
             "type": "object",
@@ -231,7 +231,7 @@ defaults.
     it won't be instantiated at all, much less populated with default
     properties.
 
-    .. code-block:: python
+    .. testcode::
 
         del schema["properties"]["outer-object"]["default"]
         obj2 = {}

docs/validate.rst

@@ -84,7 +84,9 @@ types as being acceptable for a validator object, then you should update an
 existing `TypeChecker` or create a new one. You may then create a new
 `Validator` via `jsonschema.validators.extend`.
 
-.. code-block:: python
+.. testcode::
+
+    from jsonschema import validators
 
     class MyInteger(object):
         pass
@@ -97,7 +99,10 @@ existing `TypeChecker` or create a new one. You may then create a new
 
     type_checker = Draft3Validator.TYPE_CHECKER.redefine("number", is_my_int)
 
-    CustomValidator = extend(Draft3Validator, type_checker=type_checker)
+    CustomValidator = validators.extend(
+        Draft3Validator,
+        type_checker=type_checker,
+    )
     validator = CustomValidator(schema={"type" : "number"})
 
 
@@ -129,7 +134,7 @@ which each included validator class implements.
 For example, if you wanted to validate a schema you created against the
 Draft 7 meta-schema, you could use:
 
-.. code-block:: python
+.. testcode::
 
     from jsonschema import Draft7Validator