Log Message:
Update to gipfel-0.2.6

>From ChangeLog:
* Improve image saving. It is now possible to overwrite the current
  image file.
* Install README and NEWS file to $PREFIX/share/doc/gipfel.
* Change semantics of -t option.
  -t now requires a file just as -j does.
  To generate multiple TIFF files as input to enblend, just do
  for i in *.jpg; do gipfel -s -b -t tiff/$i $i; done
  This simplifies the code and allows to parallelize stitching on
  multicore systems.
* Add simple README viewer to the Help menu.