Fix combined alters on PostgreSQL

import sys

import hashlib

import operator

from django.db.backends.creation import BaseDatabaseCreation

from django.db.backends.util import truncate_name

from django.utils.log import getLogger

from django.db.models.fields.related import ManyToManyField

from django.db.transaction import atomic

from django.utils.six.moves import reduce

logger = getLogger('django.db.backends.schema')

            # Combine actions together if we can (e.g. postgres)

            if self.connection.features.supports_combined_alters:

                sql, params = tuple(zip(*actions))

                actions = [(", ".join(sql), params)]

                actions = [(", ".join(sql), reduce(operator.add, params))]

            # Apply those actions

            for sql, params in actions:

                self.execute(