[FIX] hr_expense: tax amount computation

The tax_amount field should contain the basic amount (without tax) for base tax code. (opw 613470)
[FIX] survey: access rights error when editing

The wizard 'Edit Survey' > 'Add Question' was trowing an access rights error as the id was passed as a string instead of a real id. opw 607854
[FIX] stock: return picking, pass serial number value when returning
[FIX] web: sort with undefined value

In this awesome programming language called javascript, undefined is neither bigger nor smaller than a string. Previous code was then considering undefined values equal to any string.
This fix allows to sort in a column of a o2m field and group the undefined values together. opw 607704
[FIX] l10n_ro: backport of fix done in res_partner.py from aa76885

PR #720
[FIX] mrp_repair: invoice the actual invoice partner id