Upgrade to libvpx commit e479379a.

This version includes a critical bug fix for temporal layers.

BUG=
TEST=

Review URL: https://webrtc-codereview.appspot.com/350012

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1454 4adac7df-926f-26a2-2b94-8c16560cd09d
37 files changed