This patch creates some basic infrastructure for doing bitstream-
incompatible changes to the VP8 encoder. The key parts are:
- --enable-experimental configure switch, to enable support for this
incompatible bitstream. This switch is required to be set to enable
any "experiments"
- A list for "experiments" which translate into --enable-<experiment>
options and CONFIG_<experiment> macros.
- The high bit of the "Version" field is used to indicate that the
bitstream was produced by an experimental encoder. The decoder will
fail to decode an experimental bitstream without
--enable-experimental.
- A new "vp8x" encoder interface is created to set the experimental
bit.
- The vp8x encoder interface is made the default for ivfenc in
experimental mode.
Change-Id: Idbdd5eae4cec5becf75bb4770837dcd256b2abef
0952acb79a