Add vp9cx_set_ref to .gitignore
Add vp9cx_set_ref to .gitignore

Get rid of the 'git status' clutter when building with examples.

Change-Id: I20b715ddfc6c8ccb4993de7ebb2b4ad6df9ea437

mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,webmproject/libvpx,ShiftMediaProject/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx,Topopiccione/libvpx,webmproject/libvpx,mwgoldsmith/vpx,Topopiccione/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,Topopiccione/libvpx,webmproject/libvpx,Topopiccione/libvpx,webmproject/libvpx,mwgoldsmith/libvpx