[FIX] Bug #119 account_auto_fy_sequence now works well with the POS

Please refer to the bug report #119 for a detailed scenario of the crash.

Don't ask me why this fix solves the bug, I have no idea ! But it fixes the bug, that's the most important ! :) I hit this bug this morning (1/1/2015) when rolling out my first OpenERP POS in production... ARG !!!
I "copied" this solution from odoo-80/addons/account/ir_sequence.py : this file also uses the old API like account_auto_fy_sequence, but uses the decorator "@api.cr_uid_ids_context" above the _next() method.

Another way to fix the bug is to modify the code of odoo-80/addons/point_of_sale/point_of_sale.py line 750 in the create() method:
replace:
```
values['name'] = session.config_id.sequence_id._next()
```
by 
```
values['name'] = self.pool['ir.sequence']._next(cr, uid, [session.config_id.sequence_id.id], context=context)
```