[MRG] resolve conflict
[REF] 'product' use now move_field_many_values_to_one function.
[REF] 'hr_expense'. use now 'move_field_many_values_to_one' function;
[REF] manage fast (by sql) and slow (by orm.write function) requests
 to update fields;
[REF] update calls in 'hr_expense' and 'product' migrations scripts;
[REF] pep8.
[REF] rename 'move_field_many_values_to_one' into 'move_field_m2o';