Add getAutoCommit (sqlite3_get_autocommit)

Only exported from .Direct for now to avoid cluttering the main API with
this obscure method.  Also, the boolean "autocommit" is confusing, because
it's True when a transaction is *not* in progress.  We might want a more
intuitive public API:

    active <- isTransactionActive conn
    when active $ exec conn "ROLLBACK"

instead of:

    autocommit <- getAutoCommit conn
    when (not autocommit) $ exec conn "ROLLBACK"
Merge pull request #28 from joeyadams/getAutoCommit

Add getAutoCommit (sqlite3_get_autocommit)