[MERGE] [FIX] account_voucher: forward port of fixes from 6.1 (rev 6966)

[MERGE] [FIX] account_voucher: forward port of fixes from 6.1 (rev 6966)
When importing invoices to a bank statement the bank statement lines are created with statement date instead of today
Set the date on the created voucher in the same wizard to the statement date instead of invoice date (problematic if different period)
When creating the account moves (at bank statement confirmation), make sur the date and period of the vouncher are synchronised

bzr revid: mat@openerp.com-20140129172009-vbp5n1nco51kaly8