Fixed bug 2733

* Ref. https://github.com/easydigitaldownloads/Easy-Digital-Downloads/issues/2733.
Merge remote-tracking branch 'upstream/master'
Rewritten check on "zero price" cart items

* Check now conforms to EDD standards.
Fix tax rate description. #2690
New version of the add-on updater that doesn't check for updates on every page load
Wrap last checked in multisite check
Tweaked updater
Fix syntax error
Set the slug when viewing the changelog and don't show the update notification row in non-multisite
Fix issue wth update not showing in non-multisite
Use pre_set_site_transient_update_plugins
Version bump and changelog
Only modify comment_clauses if wp_Version is less than 4.1. #2751
Update edd_hide_payment_notes() to use pre_get_comments and type__not_in. #2751
add_action/remove_action pre_get_comments in edd_get_payment_notes(). #2751
Introduce edd_redirect_canonical() to fix #2632 and to fix #2743
Merge branch 'release/2.2' of github.com:easydigitaldownloads/Easy-Digital-Downloads into release/2.2
Add some missing capability checks
Merge pull request #2734 from daigo75/master

Fixed bug #2733
Fix undefined index type__not_in