Revert commit r22596.

Revert commit r22596.

  commit ab8610aa176c13b5e25a2d8770df28a14665e169
  Author: koorogi <koorogi@9553f0bf-9b14-0410-a0b8-cfaf0461ba5b>
  Date:   Thu Mar 18 23:13:04 2010 +0000

    The vflip filter does not need to keep ownership of a picture reference.
    Avoid creating and releasing useless extra picture references in the
    start_frame and end_frame callbacks.

    Originally committed as revision 22596 to svn://svn.ffmpeg.org/ffmpeg/trunk

The new reference creation is required when the linesizes are used by the
previous filters in the filterchain, for example as in "pad=W:H:X:Y,vflip".

Originally committed as revision 26059 to svn://svn.ffmpeg.org/ffmpeg/trunk