Fixes the annoying 100% zoom and then continuing where it was.

This way, zooming, panning etc. gets sped up quite a bit.

When executing an action starting with a semicolon, feh will
not skip to the next slide. The semicolon is not passed on to
the executing shell, of course. This is kinda ugly, but at least
it makes action handling somewhat more flexible.

Set --slideshow-delay to a negative value to achieve that. In that case, the
actual slideshow-delay will be <value> * (-1), so -D-5 sets slideshow-delay 5
seconds but starts paused.

Closes: GH-4 <http://github.com/derf/feh/issues#issue/4>