Merge pull request #261 from knowledgepoint-devs/modal

Various fixes that need to go out to kp-dev for Tim to test.
auto-join users to groups upon edis of the pre-approved emails and domains
Merge branch 'modal' of github.com:ASKBOT/askbot-devel into modal
Merge pull request #264 from knowledgepoint-devs/modal

Allow 20 questions per page option
Merge pull request #265 from knowledgepoint-devs/modal

Fixed 500 error "Related Field has invalid lookup: icontains" when
fixed negation bug in joining preapproved groups when email is validated
Merge branch 'modal' of github.com:ASKBOT/askbot-devel into modal
implemented make thread private feature
added explicit ASKBOT_PARNTER_SITE_IDS setting to the settings.py file
Merge remote-tracking branch 'upstream/modal' into modal
made it impossible to reveal identity of asker by someone else editing the question
added setting ASKBOT_AGGREGATOR_SITE_IDS for the multisite setup
added signal sending on posting question by email
fixed a bug in the Space.get_default_ask_group_id
added missing argument is_anonymous to the post.__add_revision function
Merge remote-tracking branch 'upstream/modal' into modal