Add: tutorial for progressive morphological filter
Added libboost-chrono1.53-dev to Travis CI script.
Added boost::chrono to dependency list

* Chrono was added in boost 1.47.0, so changed minimum version to match.
Added FindOpenNI2.cmake search module.

*also added a find_openni2 macro to PCLConfig.cmake.in to allow external users of PCL to find the OpenNI 2 libraries. This is a duplicate of the code in FindOpenNI2.cmake.
Created abstract Image interface for OpenNI grabbers.
Added OpenNI 2 grabber.
Stopped throwing exception on frame sync failure.

* This is not an exceptional event and always occurs for file devices. Print error message instead.
Fixed data race problem with multiple sensors

* The convertTo..PointCloud methods used statically allocated buffers to resize images, causing a data race if multiple deices tried to create point clouds simultaneously. Switched to using member buffers for each grabber.
Fixed warnings in OpenNI 2 grabberModeToOpenniMode

* Fixed assignment in conditional test
* Removed unused argument to focal length getters
* Removed 'register' keywords that do nothing.
Added OpenNI 2 viewer app to visualization module.

* Changed default viewpoint for OpenNI 2 viewer app. Needed to look down +Z axis to see point cloud.
Added HAVE_OPENNI check to people_app

* Depends on pcl/io/openni_grabber.h and does not work with OpenNI 2.x grabber yet
Move common image files to pcl/io/ during the installation; fix block alignments.
Fix: make sure point is finite before vicinity search
Merge pull request #617 from nizar-sallem/fix_region_growing

Fix: make sure point is finite before vicinity search
Merge pull request #602 from chambbj/pmf-tutorial

Add: tutorial for progressive morphological filter
Matrix transform tutorial update
Merge pull request #621 from VictorLamoine/matrixTransform

Matrix transform tutorial update
Fix: alignment issue of SupervoxelClustering
Merge pull request #625 from chia0418/fix-supervoxel-clustering-alignment

Fix: alignment issue of SupervoxelClustering
Issue #564: Fix tutorials warning