uninstall: avoid errors during uninstall

When uninstalling a module, remove the ir.model.constraint after removing the non-model records and before fields and model definition.
Without this fix, some constraint would be removed too early allowing to have broken relations and data left from removed module.
[FIX] web: many2many field handle "no_create" option
[FIX] project_timesheet: don't trigger write if there is nothing to write

Triggering an empty write could break constraint (can not update past timesheet) (opw 606963)
[FIX] document_page: allow other users than administrator to create menu to a static page

User should be at least have Configuration settings group to be allowed to create actions. Basic document page users do not have this rights, therefore we temporary give superuser_id to create the action

This is related to rev 133c5033a092845e462b894c0d7739191480c709
[IMP] stock: when checking the state of the product, do not recompute the quantity on every move but only the one currently browsing (optiomisation)
[FIX] ir_cron: use the same search criteria as when listing job to excecyte when acquiring the ock on the job before its execution to prevent running already executed job

Backport of fix made in trunk
[FIX] orm: do not resize unlimited char fields
[FIX] orm: do not recompute m2o stored function field at read.

The get() method of m2o function fields is used for 2 different things:
 - call the function defining the m2o
 - get the name_get representation of the value

Until this pathc, only the first case was handled, resulting to a useless
recomputation of the field when reading it.
Merge pull request #404 from odoo-dev/7.0-norecomputestoredm2ofuncfields-chs

[FIX] orm: do not recompute m2o stored function field at read.