[FIX] web: list views: bubble up failed deferreds.
[FIX] web: list view group: always call post_render method
[MERGE][FIX] web: fix race condition in BufferedDataset.

Backport of saas-2 commit 3867 nicolas.vanhoren@openerp.com-20131107112017-7omd01ocvnbzx9m6