python 3k version does not accept Decimal objects as bind parameters

[Mike Bayer]

test case passes with python 2k, fails with the latest hg tip at http://hg.pybrary.net/pg8000-py3/ :

from pg8000 import dbapi
from decimal import Decimal

connection = dbapi.connect(user='scott', host='localhost', database='test', password='tiger')
cursor = connection.cursor()

cursor.execute("""
CREATE TABLE numeric_table (
    numericcol NUMERIC(10, 2)
)
""")

# works on both Py2K/Py3K
cursor.execute("""INSERT INTO numeric_table (numericcol) VALUES (%s)""", [3.5])

# works on Py2K, fails on Py3K
cursor.execute("""INSERT INTO numeric_table (numericcol) VALUES (%s)""", [Decimal('3.5')])