jpegpay: consider header len when calculating payload len

Fixed https://bugzilla.gnome.org/show_bug.cgi?id=726777
v4l2src: Fix support for mpegts streams

It seems that GStreamer's mpegts elements (tsdemux, tsparse) require caps
`video/mpegts,systemstream=true`.  As far as I can see the significance
of systemstream is to indicate that this is a container format rather than
an elementary stream.  As this is the case (and I can't understand how it
could not be the case with mpegts) I add systemstream=true to v4l2src's
caps.

This allows v4l2src to be linked with tsdemux for playback from my
Hauppauge HD-PVR with the pipeline:

    v4l2src ! queue ! tsdemux ! video/x-h264 ! decodebin ! xvimagesink

In combination with the next commit this fixes using Hauppauge HD-PVR with
GStreamer 1.0+.
v4l2: Fix support for caps without width, height, framerate or format

For format like mpegts, width and height is rarely in the negotiated caps. This
patch fixes failure when setting format, and prevent introducing width, height,
framerate and format to the caps when fixating.

https://bugzilla.gnome.org/show_bug.cgi?id=725860

Conflicts:
	sys/v4l2/gstv4l2object.c
v4l2object: Don't validate dimension for encoded format

We set the dimensions just in case but don't validate them
afterwards. For some codecs the dimensions are *not* in the
bitstream, IIRC VC1 in ASF mode for example.

https://bugzilla.gnome.org/show_bug.cgi?id=720568

Conflicts:
	sys/v4l2/gstv4l2object.c
tests: souphttpsrc: use SoupKnownStatusCode if needed

From libsoup docs:

Prior to 2.44 SoupStatus was called SoupKnownStatusCode,
but the individual values have always had the names they
have now.

Fixes:
  https://bugzilla.gnome.org/show_bug.cgi?id=727329