[FIX] models: do not prefetch fields to recompute, and recompute once only

The method _prefetch_field() was accidentally prefetching fields to recompute;
which was skipping the actual recomputation, since a value was put in cache.
But sometimes the field's value was fixed by an extra recomputation of the
field.  Here we remove the extra recomputation and fix the cache corruption.
[IMP] models: do not use compute methods to determine default values anymore

Compute methods could give results that should not be considered as default
values.  For instance, a related field usually defaults to a null value, which
is then set to the field with its inverse method by create().  This may violate
a non-null constraint if the original field is required.  Therefore, compute
methods are no longer used to determine default values.
[FIX] models: on update, call inverse function on field even when it is stored

The inverse function of a stored computed field was not called when creating or
writing on a record with such a field.
[FIX] web: oe_navbar compatibility on IE11
[FIX] stock_picking_wave: removed obsolete many2many widget from stock_picking_wave_view
[FIX] mail: followers widget was broken

This was probably due to 35f5fb46e78aef1feda4d9cfddd93bd356bdca28.
[FIX] GeoIP - allow to specify the path to GeoIP in the server config.

--geoip_db='the_path'  which can be used via openerp.tool.config['geoip_database']
[FIX] read_group: date format: use natural year along with month names, do not mix with ISO week-year

The ISO week-year notation can produce confusing values
when the first week of the year is so short that it
becomes week 0 and is considered the last week of the
previous year, depending on the locale.

For instance, using ISO notation:
  'W53 2015' == dates.format_date(
      date(2015,1,1), format="'W'w YYYY", locale='en_GB')
  'W53 2005' == dates.format_date(
      date(2006,1,1), format="'W'w YYYY", locale='de_DE')

This is surprising but actually valid.

However it definitely yields wrong output when combined with
months formats:
  'January 2014' == dates.format_date(
      date(2015,1,1), format="MMMM YYYY", locale='en_GB')

As a result we must always use `y` to denote the year in
any date format, *except* when it is combined with the
week number `w`, in which case we must use `Y`.

See the documentation at:
   http://babel.pocoo.org/docs/dates/#date-fields
[FIX] Use currency of pricelist when creating PO from procurement
Merge pull request #3061 from odoo-dev/8.0-wmspocurrency-jco

[FIX] Use currency of pricelist when creating PO from procurement
[FIX] website.snippet: can't edit content of the banner. (+ better fix for backward compatibility)
Merge remote-tracking branch 'upstream/8.0' into 8.0