Whenever a user navigates away, all ajax calls will fail with the same
result like a cross-domain redirect (SSO). To distinguish these cases,
we need to detect whether the error is a result of the user navigating
away. For this, we introduce a new flag that will be set in
"beforeunload".
Additional handling was required for false positives in case "beforeunload" is
used (ex: cancelled upload) and the user cancelled the navigation.
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