facedetect: set maximum feature size to 0x0

This disables the "max feature size" feature. The current configuration
is totally busted: The max feature size is hard-coded to 2 pixels more
than the user-supplied min feature size which pretty much means you need
to guess the size of the person's face to within a few pixels to get the
code to find it.

https://bugzilla.gnome.org/show_bug.cgi?id=722158
faceblur: set maximum feature size to 0x0

Previously faces would only be detected if they were at least 30x30 pixels
large and at most 32x32 pixels. We keep the minimum setting (maybe needs
a property as in facedetect) but disable the maximum feature size.

See https://bugzilla.gnome.org/show_bug.cgi?id=722158
amcvideodec: Add the divx variant for mpeg4 video

Looks like all the mpeg4 video decoders also accept the divx
variants. So we better add those caps too

https://bugzilla.gnome.org/show_bug.cgi?id=711163