Add random color mode for "label" field.

This allows to get a colorful image where different labels are painted
with random colors.

Unit tests and pcd2png tool are updated accordingly.
Add more documentation for PointCloudImageExtractor.
Add: ability to paint a text in ImageViewer
Merge pull request #204 from taketwo/png-io

Add a generic `savePNGFile()` function
Merge pull request #293 from nizar-sallem/add_text2

Add: ability to paint a text in ImageViewer
Remove reference to openni-dev in pkg-config files.

OpenNI packages are not currently shipped with any pkg-config
files. Furthermore, Debian packages libopenni-dev and openni-dev are
currently not coinstallable and provide pkg-config files with
different namings. To workaround these issues, this patch disables
OpenNI check in pkg-config files.

This partially solves issue #221.
Merge pull request #295 from stanislas-brossette/master

Remove reference to openni-dev in pkg-config files.
Merge pull request #297 from georgebrindeiro/patch-1

Added missing word and link
Allow pcl to be built against system metslib

This patch allows PCL to build against a system installed metslib
where available.  It uses pkgconfig to try to discover metslib.pc,
and when both are available HAVE_METSLIB is set to ON and the
include paths are modified to use metslib's location as discovered
by pkgconfig.  When pkgconfig and/or metslib is not found, cmake
will continue to use the bundled version of metslib as before.
Whitespace cleanup in registration/CMakeLists.txt

While making modifications for metslib, I noticed that there was
some mixed use of tabs and spaces for intentation.  I normalized
them all to 4 spaces per tab and made the indentation of all of
the "set" blocks consistent.
Merge pull request #282 from mszarski/patch-2

NURBS Cylinder Fit Axis Initialization
Merge pull request #262 from taketwo/fix-data-references

Modify tutorials to point to the new data sources
New Version 1.7.1
reformatted according to PCL coding style
Fix compiling error of deprecated template.
vtkRegressionTestImage.h causes missing header compiler error with VS2012 vtk6 without test build turned on. It is not used at all, so just remove it.
Code for MomentOfInertia feature class
Tests for MomentOfInertia feature implementation
Tutorial for MomentOfInertia feature class
Code for RoPS feature