Failed adaptation for None in composite types

microprotocols_adapt has a fast path returning NULL on None. This is wrong: it should return an object conform to ISQLQuote. It goes unnoticed because _mogrify has a fast path not calling microprotocol_getquoted, but the bug emerges trying to adapt a record containing NULL.

In [6]: cur.mogrify("""select %s;""", [ tuple((1,'hi',None)) ])---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)

/home/piro/dev/psycopg2/<ipython console> in <module>()

/home/piro/dev/psycopg2/build/lib.2.6/psycopg2/extensions.pyc in getquoted(self)
    123             if hasattr(obj, 'prepare'):
    124                 obj.prepare(self._conn)
--> 125         qobjs = [str(o.getquoted()) for o in pobjs]
    126         return '(' + ', '.join(qobjs) + ')'
    127

It can be fixed by:

1. dropping the special case in microprotocol_adapt and adding an adapter such as:

# untested
extensions.register_adapter(type(None), lambda x: exteions.AsIs("NULL"))

it would still be a fast path in mogrify, but would allow uniform treatment of None in composite types;

1. (I mean 2 but markdown sucks) Put a different fastpath in adapt: always return the same AsIs("NULL").

2. (three) adding a special case to SQL_IN. No, I don't like it. This is the solution currently adopted by adapter_list.

Note: grep -r '"NULL"' psycopg reveals that AsIs adapts None to "NULL". This is either unnecessary or we can use that... in either case we are a little bit schizophrenic.