Make set_reference control API work in VP9 and VP10

Moved the API patch from NextGen to NextGenv2 and also added this
API to VP10. An example was included. To try it, for example, run
the following command:
$ examples/vpx_cx_set_ref vp10 352 288 in.yuv out.ivf 4 30

Change-Id: Ib56bc3d365e530cfc8d859a13ddbf4c007907b81
11 files changed