[IMP] add an index on account_move_line(date, id)

fixes https://launchpad.net/bugs/1311004
Merge pull request #417 from gurneyalex/7.0-fix_1311004_account_move_line_index-afe

[IMP] account.move.line: extra index on (date, id) corresponding to the default _order, courtesy of @gurneyalex.

 Fixes https://bugs.launchpad.net/openobject-addons/+bug/1311004