[FIX] M2m tags field wrong height count when field in nonactive notebook page at load time.
[FIX] bugs discovered by failing onwrite test case

Following xmo@openerp.com-20130607120355-x3poxy2ar2bpqqvw:

* add_ids should not add ids which are already in the dataset, this
  leads to duplicates which the web client does not overly like

* methods which add or remove records should not manipulate
  dataset.ids as well as that's now automatic (on_write feature)

* record add should only insert the id in the dataset on non-false ids
  (e.g. list edition uses "pending" record with false id during
  creation, then sets the id it got from create() call)
[FIX] css: removed the forced left alignment of dropdown menu on the calling element, as it prevented correct display of the top right drop down menu when it's content was larger than the user name