Merge commit '2d09b36c'

* commit '2d09b36c':
  doc/platform: Add info on shared builds with MSVC
  doc/platform: Move a caveat down to the notes section
  ARM: reinstate optimised intmath.h
  ffv1: update to ffv1 version 3

Conflicts:
	doc/platform.texi
	libavcodec/ffv1.c
	libavcodec/ffv1.h
	libavcodec/ffv1dec.c
	libavcodec/ffv1enc.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>