[FIX] delivery: display the label of the field number_of_packages

Fixes #4011
[FIX] Correct floating number handling for _procure_orderpoint_confirm

Fixes comparison with min_quantity orderpoint in scheduler - basic floating
point math issue in procurement scheduler when comparing current quantity
with orderpoint minimum quantity. In certain cases floating point comparison
could result in e.g 400.0 < 400.0 == True due to typical floating point
comparison issues, as Odoo doesn't use Decimal types where the issue
doesn't exist.

Fixes early exiting out of the loop cycle, in case qty is already near zero.
Fixes the new procurement creation check, to not do that if it's close
enough to zero already, to be considered a floating point math error, not
really non-zero.

These combined (or at least the last one) avoid each supply_method == buy
pending in draft PO's getting a zero quantity extra procurement order each
time the scheduler runs. Otherwise there could be hundreds of zero quantity
procurement orders pending, which makes the confirming of the PO take hours,
due to creating hundreds of stock moves for each order line.

Use float_compare helper to solve all these with floating point type for now,
instead of the more evasion possibility of converting to Decimal module.
Two potential bad comparisons remain, add FIXME notes for now until further
analysis.

Also: Float rounding on reste when comparing and on the procurement qty
[FIX] Fix floating point handling in purchase _prepare_order_line_move

Without this better floating point handling, an extra stock move might
be created for zero quantity for some order lines upon PO confirmation,
because qty is equal to something closer to e.g 1.14e-13, but this is
larger than 0, so it creates a stock.move, which gets rounded too late
to 0.0

Closes #3346
[FIX] Fix wrong unit price on invoice genereted by stock picking when uos is used

[IMP] Rounding not necessary
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64