Relax window.name clearing protection for page refresh

In #16620 (closed), the torbutton patch was ported to a Firefox patch (originally legacy/trac#3414 (closed)). The purpose of this patch is described in section 4.5.13 of the design doc. However, the goal of these patches is preventing cross-origin linkability, unfortunately the current implementation affects same-origin requests, as well. In particular a webapp may use window.name for storing session information, and when the page is reloaded window.name is cleared.

The current patch is a9bf408f