The channel module now keeps track pending ajax requests and has an
abort_all function to angle all pending requests.
(imported from commit 4e78ab24d2295bd67de5633e3a200dfa489825b1)
We've seen in our error logs browser clients that were constantly
retrying requests to our server after the user logged out in one tab
but didn't close another.
(imported from commit 68dd8d9e618083bc116ae3a96dbcc78fa9301bba)