VTK6 cmake fixes
VTK6 code fixes. VTK5 backward compatibility
removing SRC/internal.h from INCLUDE/.../kinfu.h
no need for include/../impl/cyclical_buffer.hpp, moving code to cyclical_buffer.cpp. Removing last reference from include/ to src/, too.
removing safe_call.h and internal.h references from tools/
added definition of pcl::simulation::Scene::clear()
Add: create local 2D grid over input point cloud and downsample to minimum z values per grid cell
Add: simple tool to compute Hausdorff distance between two point clouds
Update: avoid error with redefinition of struct by renaming it
Corrected typo in octree.doxy
Corrected typos in features.doxy
Corrected typos in sample_consensus.doxy
Fix of broken links in sample_consensus.doxy
Corrected typo in keypoints.doxy
Fixed broken link to the picture in the surface.doxy
Use libreoffice's PPA to get latest Doxygen on Travis

The version that is packaged for Ubuntu 12.04 is rather old and does not
support Markdown.
Addition of SACMODEL_CIRCLE3D and SACMODEL_CONE links and descriptions
Deleted the version number of PCL in sample_consensus.doxy
adding color supported GICP (for Details see http://www.is.uni-due.de/fileadmin/literatur/publikation/korn14visapp.pdf)
unit test for gicp6d