vigra.cmake: Updated git tag.
Commented out libxml2 test step because it fails on OSX???!!
vtk.cmake: Explicitly provide the locations of libpng, libtiff, libjpeg, and libz
ilastik.cmake: When checking out ilastik, do a git fetch first.
Merge commit '86aeddba8ff5b965d98f9089f2ee5ad918110187' into fix/OSX10.9

Conflicts:
	libxml2.cmake
	vtk.cmake