New: trajkovic and hedley detector 2D
New: port of Trajkovic and Hedley detector to pure geometry
Fix: a silly bug in normals diff computation
Add: pcl_ni_trajkovic application to detect Trajkovic 2D/3D points from OpenNi device
Fix: removal of unused argument and normals_->resize statement
Add savePNGFile function for histograms.

Render the histogram using vtk offline and then save the image to png
file.
PCDGrabberImpl: Add mutex to avoid reentry in trigger()/readAhead() and the resulting race condition.
Add CentroidPoint class
Add computeCentroid() functions that use CentroidPoint
Extract centroid-related tests from test_common.cpp

There are quite a number of functions dealing with centroid, mean, and
covariance computation. They all are grouped in 'common/centroid.h'
header. Therefore it makes sense to group their corresponding test
functions in a separate file. Hence creation of 'test_centroid.cpp'.
Add unit tests for CentroidPoint and computeCentroid()
Fix obscure MSVC error
Merge pull request #409 from nizar-sallem/trajkovic

Trajkovic
Merge pull request #528 from sksavant/histogram-save-pr

Add savePNGFile function for histograms.
Merge pull request #582 from j-oberlaender/master

PCDGrabberImpl: Add mutex to avoid reentry in trigger()/readAhead() and the resulting race condition.
Merge pull request #586 from taketwo/add-centroid-point

Add a new `CentroidPoint` class
Merge pull request #593 from taketwo/fix-msvc-stl

Fix obscure MSVC error