The 5-layer encode must have a keyframe every 16 frames.

The KF flag was being reset after the encode of the first
frame, which it should not do for the 5-layer case
(mode=6).

Change-Id: I207d6e689d347fe3fd1075b97a817e82f7ad53b9

Added new 2 and 3 layer prediction frame patterns to
vp8_scalable_patterns.c and modified the coding
parameters.

Change-Id: I18798fd7326a79d2ad1e1d5b6c26f5516b6d247f

When running multi-layer (ML) encodes and dynamically
changing coding parameters on the fly (e.g. frame
duration/rate, bandwidths allocated to each layer)
the encoder would not produce sensible output.

In certain cases the rate targeting would be
hideously inaccurate.

These fixes make it possible to change these coding
parameters correctly and to maintain accurate control
of the rate targeting.

I also added the specification of the input timebase
into the test program, vp8_scalable_patterns.c.

Patch 2: Moved declaration to appease MS compiler)

Change-Id: Ic8bb5a16daa924bb64974e740696e040d07ae363

Added the ability to create rate-targeted, temporally
scalable, VP8 compatible bitstreams.

The application vp8_scalable_patterns.c demonstrates how
to use this capability. Users can create output bitstreams
containing upto 5 temporally separable streams encoded
as a single VP8 bitstream.
(previously abandoned as:
I92d1483e887adb274d07ce9e567e4d0314881b0a)

Change-Id: I156250a3fe930be57c069d508c41b6a7a4ea8d6a