Added a pull function in the gstpad. Modified the videosink to implement the pull. This function allows a source elem...

Original commit message from CVS:
Added a pull function in the gstpad. Modified the videosink to implement
the pull. This function allows a source element to request a buffer
from the destination. This is much more efficient because the
videosink can then pass a buffer with SHM to the element, which does
not require an aditional memcpy.
removed scaling from the videosink. I need something better.