Better feature detection for assimp version

The unified headers were introduced in Assimp 2.0.1150, so checking for Assimp 3.0.0 is not quite the best solution.

See https://github.com/assimp/assimp/commit/6fa251c2f2e7a142bb861227dce0c26362927fbc
Use VERSION_LESS instead of STRLESS 

The version comparison routines were added in cmake 2.8.0
Merge pull request #711 from cottsay/hydro-devel

Better feature detection for assimp version
Merge pull request #716 from acornacorn/hydro-devel

Make rviz work with Ogre 1.10
render in stereo if supported

This adds stereo rendering support to Rviz.

To see stereo Rviz must be built against a version of Ogre that was
built with the OGRE_STEREO_ENABLE config option enabled.  This option
is currently only supported in the branch of Ogre found here
  https://bitbucket.org/crefvik/ogre
or here
  https://bitbucket.org/acornacorn/ogre

To see stereo you will need:
- a stereo monitor
   (I am using an ASUS VG278H)
- a video card that supports quad-buffer stereo.
   (I am using an NVIDIA Quadro K4000)

To build rviz with stereo support:
remove debian-installed ogre:
	sudo apt-get remove libogre-1.7.4 libogre-dev
build the stereo-enabled ogre:
	cd $HOME
	mkdir my-ogre
	cd my-ogre
	hg clone https://bitbucket.org/crefvik/ogre
	mkdir build
	cd build
	cmake -DOGRE_FULL_RPATH=ON -DOGRE_BUILD_STEREO_SUPPORT=ON ../ogre
	sudo make install
then build rviz as usual using catkin_make
	cd $HOME
	mkdir -p my-workspace/src
	cd my-workspace/src
	git clone https://github.com/ros-visualization/rviz.git
	cd ..
	catkin_make
Run rviz
	roscore & rosrun rviz
If your HW supports stereo you should see a double image (stereo when
wearing the glasses).  Properties in the ViewController panel can be
used to set eye-separation, focal-distance, to swap the eyes, and to
disable stereo.

If stereo is supported on your hardware, rviz will automatically
render in stereo unless you either
- disable stereo by unchecking the "Enable Stereo Rendering" property in the view panel.
- use the --no-stereo commandline option (stereo properties will be hidden)

If stereo is not suppported on your hardware, rviz will not render in
stereo and the stereo-related properties will be hidden.