Bug 875719 - Simplify and correct the mechanism of handling call state change event, r=gyeh

1. Remove variable mCurrentCallIndex and replace with using function FindFirstCall(aState)
2. Remove unused variable index and callArrayLength
Bug 871438 - Reset value when file transfer session starts, r=gyeh

When the transferring session was stopped, mBodySegmentLength wouldn't reset
to 0, and that would impact the next transferring if the first packet of the
next transferring doesn't contain header Body or EndOfBody, which would invoke
ExtractPacketHeaders() and refresh mBodySegmentLength in the function.
Bug 875208 - Check blob last modification date before sending it through IPC. r=gene.lian
Merge mozilla-central and birch
Merge latest green birch changeset and mozilla-central