[IMP] stock: Optimize stock_move.setlast_tracking()

When setlast_tracking is called on a large number of moves in a picking
(e.g.  when splitting moves in a picking), the time to complete grows
exponentially.  The reason is that it loops over all the moves of
a picking, even if it keeps only the last tracking.

The method now uses a search() with a limit so it doesn't need to browse
all the moves.

Added test to check the behaviour of setlast_tracking
Fixes #2448
[INP] portal_sale: remove buggy context

Even if this should never be used in normal portal environment, if a user with enough access rights tries to create an invoice, this would crash. We don't need context here (opw 612591).
[FIX] product,float_utils: perform ceiling via float_round with new rounding_method UP

Modified product ceiling() to use float_round() with special mode
for rounding UP (away from zero), avoiding pathological cases where
float representations errors were ceiling to the superior unit.

Also added correspding tests for rounding_method=UP

Fixes issue #1125, and replaces PR #1126.
[FIX] product: _compute_qty: first round before ceiling, to avoid pathological cases

Fixes problem when we try to sell 12 units of a product and change it to 1 dozen,
the algorithm was then trying to recompute the original amount and was getting
12,0000048 as a result which was then passed to the ceiling method, getting 13.0!

See also previous commit and issue #1125, PR #1126
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32