Update ply_io.cpp

Reading a binary PLY file with faces and "vertex_indices" property crashes, if only a PointCloud is provided. Since the polygons_ member is set to 0 and untouched otherwise.

Worked in PCL 1.6, doesn't work right now with 1.7.1.

The ply2pcd sample program provided with PCL crashes as well.
Fix some whitespace issues
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: alignment issue of SupervoxelClustering
Merge pull request #625 from chia0418/fix-supervoxel-clustering-alignment

Fix: alignment issue of SupervoxelClustering
Issue #564: Fix tutorials warning
Merge pull request #627 from VictorLamoine/issue564

Fix tutorials warnings (fixes #564)
fix progressive morphological filter to stop at the max window size
Merge pull request #630 from chambbj/fix-progressive-morphological-filter

fix progressive morphological filter to stop at the max window size
fix error in PFH tutorial