[FIX] core: avoid infinite recursive loop.

`function` fields are fully copied via `copy.copy()`.
`copy.copy()` *do not* call `__init__` after object creation; then
restore the state via `__setstate__()` or by updating `__dict__` or via
`setattr()` when the object uses `__slots__`.

As `__init__` is not called, the newly created object does not have any
`_args` attribute. This lead to a recursive call of `__getattr__ when
`copy.copy` check the existance of `__setstate__` attribute.

When break this loop by forbidding explicitly by checking the attribute
name accessed (We cannot check the presence of `_args` in `__dict__`
because we uses `__slots__`).

See http://bugs.python.org/issue5370
Fixes #6037
opw:633109

openerp/osv/fields.py

@@ -151,6 +151,8 @@ class _column(object):
 
     def __getattr__(self, name):
         """ Access a non-slot attribute. """
+        if name == '_args':
+            raise AttributeError(name)
         try:
             return self._args[name]
         except KeyError: