Use py.builtin.callable

This restores compatibility with Python 3.0/3.1

Author: The-Compiler

_pytest/_code/code.py

@@ -235,7 +235,7 @@ def ishidden(self):
             except KeyError:
                 return False
 
-        if callable(tbh):
+        if py.builtin.callable(tbh):
             return tbh(self._excinfo)
         else:
             return tbh