Minor py3.3 fixes

bin/hy

@@ -120,7 +120,7 @@ def koan_macro(tree):
 try:
     readline.read_history_file(history)
 except IOError:
-    open(history, 'wa').close()
+    open(history, 'a').close()
 
 readline.parse_and_bind("tab: complete")
 

hy/completer.py

@@ -20,7 +20,11 @@
 
 import hy.macros
 import hy.compiler
+
+try:
     import __builtin__
+except ImportError:
+    import builtins as __builtin__ # Py 3.3
 
 
 PATH = [hy.compiler._compile_table,
@@ -28,7 +32,7 @@ PATH = [hy.compiler._compile_table,
         __builtin__.__dict__]
 
 
-class Completer:
+class Completer(object):
     def __init__(self, namespace=None):
         if namespace and not isinstance(namespace, dict):
             raise TypeError('namespace must be a dictionary')