Test suite fails using SQLite in memory database

[Russell Keith-Magee]

Ned Batchelder reports that when using the SQLite backend on [3708], the test_client modeltests closes the database cursor, which causes all the database schema to be lost.

Modifying backends/sqlite3/base.py to the following:

def close(self):
    from django.conf import settings
    if self.connection is not None and settings.DATABASE_NAME != ":memory:":
        self.connection.close()
        self.connection = None

fixes the problem.

[Russell Keith-Magee]

(In [3723]) Fixes #2658 -- Modified SQLite cursor close() method for in-memory databases, making the lifespan of an in-memory database equal to the life of the process, rather than the life of the cursor. Thanks, Ned Batchelder.