Enhance django postgresql orm for trigram search

# tested with django 1.6.10

# 1. Activate pg_trgm
# Create an empty migration (South) and add:
    def forwards(self, orm):
        db.execute("CREATE EXTENSION IF NOT EXISTS pg_trgm")
        db.execute("CREATE INDEX model_field_trgm_idx ON app_model USING gin (field gin_trgm_ops)")

    def backwards(self, orm):
        db.execute("DROP INDEX IF EXISTS model_field_trgm_idx")
# Of course, replace *app*, *model* and *field* by your application, modelname and fieldname

# 2. Add the following code in your application __init__
    # -*- coding: utf-8 -*-
    from django.db.backends.postgresql_psycopg2.operations import DatabaseOperations

    def trgm_search(self, fieldname):
        t = "{0} %% %s".format(fieldname)
        return t

    DatabaseOperations.fulltext_search_sql = trgm_search

# 3. Now, you can simply use:
model.objects.filter(field__search="abc")