Use py3k compatible .__getattr__() code

From the python-dev thread it seemed like using
object.__getattribute__(self, 'name') is the cleanest way of
implementing a class wich uses .__getattr__() and should be
pickelable.  That only works on new-style classes so this also turns
HookProxy into a new-style class on py2.

This also re-writes the test to not use cPickle so it runs on py3k.

_pytest/capture.py

@@ -238,10 +238,7 @@ class EncodedFile(object):
         self.write(data)
 
     def __getattr__(self, name):
-        if hasattr(self, "buffer"):
-            return getattr(self.buffer, name)
-        else:
-            raise AttributeError("attribute buffer of %r not set" % self)
+        return getattr(object.__getattribute__(self, "buffer"), name)
 
 
 class MultiCapture(object):