Fix tests regarding contract type conversion.

docs/frequently-asked-questions.rst

@@ -379,7 +379,7 @@ In this example::
     }
 
     contract A {
-        address child;
+        B child;
 
         function test() public {
             child = (new B).value(10)(); //construct a new B with 10 wei

docs/types.rst

@@ -901,7 +901,7 @@ for each ``_KeyType``, recursively.
         function f() public returns (uint) {
             MappingExample m = new MappingExample();
             m.update(100);
-            return m.balances(this);
+            return m.balances(address(this));
         }
     }