Bug 868891 - Fix regression introduced by Bug 860934. r=dougt

Bug 860934 removed the use of fully qualified paths when communicating between the
parent and child processes. This patch fixes one of the spots that got missed.
Merge m-c to birch.
Bug 853350 - Follow up. Make windows build.
Bug 861894 - Avoid apps to schedule new offline cache downloads while device free space is low. r=honzab
Bug 861894 - Avoid apps to schedule new offline cache downloads while device free space is low. Tests. r=honzab
Bug 861920 - Avoid apps to write in its local storage while device free storage is low. r=honzab
 Bug 861920 - Avoid apps to write in its local storage while device free storage is low. Tests. r=honzab
Bug 846133 - Store FHR state in a file; r=rnewman

Preferences aren't robust. So, we're using a file.
Bug 861903 - Hook IndexedDB up to low disk space notifications. r=janv.
Backed out 4 changesets (bug 861920, bug 861894) for mochitest failures.

Backed out changeset 69fcebb24095 (bug 861920)
Backed out changeset c39ceb11cb76 (bug 861920)
Backed out changeset d0aa77e7825b (bug 861894)
Backed out changeset 81e072111e98 (bug 861894)
Bug 861903 - Bustage fix.
Bug 861903 - Bustage fix.
Bug 861903 - Bustage fix.
Merge central into services
Bug 861903 - Disable faulty test until it can be fixed.
Bug 861903 - Disable faulty test until it can be fixed with 100% less bustage.
Bug 863732 - Use RTC wakeup to monitor WebSocket connection. r=jlebar
Bug 830213 - Modify function NotifyStatusChanged in BluetoothHfpManager, r=echou
Bug 858416 - Create a composite device storage interface. r=dougt
Merge birch to m-c.