Relative support of old versions of SQLite that do not understand "PRAGMA read_uncommitted"

Mac OS X 10.4 ships with SQLite 3.1.3. Since SQLAlchemy 0.7, I am not able to use this version of SQLite anymore. Here is a test failure (I get the same error for all tests that involve SQLite):

$ ./sqla_nose.py test.dialect.test_sqlite:TestTypes.test_boolean
E
======================================================================
ERROR: test.dialect.test_sqlite.TestTypes.test_boolean
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Traceback (most recent call last):
  File "/Users/damien/env/lasco/lib/python2.7/site-packages/nose-1.0.0-py2.7.egg/nose/case.py", line 187, in runTest
    self.test(*self.arg)
  File "/Users/damien/dev/sqlalchemy/./test/dialect/test_sqlite.py", line 44, in test_boolean
    meta.drop_all()
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/schema.py", line 2401, in drop_all
bind.drop(self, checkfirst=checkfirst, tables=tables)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/engine/base.py", line 1976, in drop
    connection=connection, **kwargs)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/engine/base.py", line 2004, in _run_visitor
    conn = self.contextual_connect(close_with_result=False)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/engine/base.py", line 2098, in contextual_connect
    self.pool.connect(),
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/pool.py", line 218, in connect
    agent = _ConnectionFairy(self)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/pool.py", line 370, in __init__
    rec = self._connection_record = pool._do_get()
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/pool.py", line 557, in _do_get
    c = self._create_connection()
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/pool.py", line 174, in _create_connection
    return _ConnectionRecord(self)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/pool.py", line 258, in __init__
    pool.dispatch.first_connect.exec_once(self.connection, self)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/event.py", line 265, in exec_once
    self(*args, **kw)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/event.py", line 274, in __call__
    fn(*args, **kw)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/engine/strategies.py", line 161, in first_connect
    dialect.initialize(c)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/engine/default.py", line 181, in initialize
    self.get_isolation_level(connection.connection)
  File "/Users/damien/dev/sqlalchemy/./lib/sqlalchemy/dialects/sqlite/base.py", line 508, in get_isolation_level
    value = cursor.fetchone()[0](0)
TypeError: 'NoneType' object is not subscriptable

----------------------------------------------------------------------
Ran 1 test in 0.010s

FAILED (errors=1)

This is because "PRAGMA read_uncommitted" is ignored by this old version of SQLite:

  sqlite> PRAGMA read_uncommitted;
  sqlite>

SQLite does not return any result at all, hence the error in the traceback. The work around is obvious (see attached patch against the tip).

I think that this pragma directive has been added in SQLite 3.3.0 according to the changelog. SQLite 3.3 has been released in January 2006 so I would understand if you rejected this bug as "Won't fix, you need to upgrade". On the other hand, this is the sole bug I have encountered so far on a small project since I switched to SQLAlchemy 0.7 (granted, I do not do anything fancy there).

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