[FIX] hr_payroll: replace non-ascii help string by unicode literal

Would trigger a UnicodeWarning when looking to update ir.model.fields
in _field_create (final loop): the unicode value from the database
would be compared with the str value from the model, the str would
fail to decode triggering the warning and assuming a False test,
probably also triggering an unnecessary database UPDATE.

addons/hr_payroll/hr_payroll.py

@@ -734,7 +734,7 @@ class hr_salary_rule(osv.osv):
         'name':fields.char('Name', required=True, readonly=False),
         'code':fields.char('Code', size=64, required=True, help="The code of salary rules can be used as reference in computation of other rules. In that case, it is case sensitive."),
         'sequence': fields.integer('Sequence', required=True, help='Use to arrange calculation sequence', select=True),
-        'quantity': fields.char('Quantity', help="It is used in computation for percentage and fixed amount.For e.g. A rule for Meal Voucher having fixed amount of 1€ per worked day can have its quantity defined in expression like worked_days.WORK100.number_of_days."),
+        'quantity': fields.char('Quantity', help=u"It is used in computation for percentage and fixed amount.For e.g. A rule for Meal Voucher having fixed amount of 1€ per worked day can have its quantity defined in expression like worked_days.WORK100.number_of_days."),
         'category_id':fields.many2one('hr.salary.rule.category', 'Category', required=True),
         'active':fields.boolean('Active', help="If the active field is set to false, it will allow you to hide the salary rule without removing it."),
         'appears_on_payslip': fields.boolean('Appears on Payslip', help="Used to display the salary rule on payslip."),