This is based on:
	commit 30f51509
	Author: Mans Rullgard <mans@mansr.com>
    		h264: allow cropping to AVCodecContext.width/height

The above commit is not taken as is as its buggy (incorrect handling of
the interlaced case) and didnt apply cleanly.

Fixes ticket156
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>