Updated scons to work with the ffmpeg binaries in lib/windows/gcc again. Also fixed a bug reported by Debolaz on irc. Blender's internal avi reading (which can only read simple formats like motion jpeg) was telling the video code it could read all avis, without checking their codec. To fix this, I copied AVI_open_movie(), and modified it to to replace AVI_is_avi(). Now it properly checks the codec, and validates the header.