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.
Code for MomentOfInertia feature class
Tests for MomentOfInertia feature implementation
Tutorial for MomentOfInertia feature class
Code for RoPS feature
Tests for RoPS feature implementation
Tutorial for RoPS feature class
Clears inlier indices if save_inliers_ is true so that the same rejector instance
can be used in different runs. Side note: user code checking the returned inlier indices size
might be able to detect if consensus was found. Note that without this, when no consensus is found,
the filtered correspondences are equal to the input correspondences.
Added explicit overloads and instatiations for pcl::PointXYZ.
Supervoxel clustering can then be used with XYZ data.
Fixed a problem where keys would change and no longer match for certain leaves
Fixed to make octree static
Just changed spacing
Fix: intel compiler doesn't like typenamed references
add missing OPT_DEPS to io for pcap/png
Merge pull request #336 from v4hn/io-opt-depends

add missing OPT_DEPS to io for pcap/png
Merge pull request #333 from nizar-sallem/fix_icc

Fix: intel compiler doesn't like typenamed references
Merge pull request #332 from jpapon/fix_octree_adjacency

Fix octree adjacency bounding box calculation
Merge pull request #323 from arbeitor/master

Clears inlier indices if save_inliers_ is true so that the same rejector...
Simplified pcl::Registration::getFitnessScore()

getFitnessScore() is implemented quite complicated. To transform the input,
transformPointCloud() can be used and the point-to-point distance is allready
given by nn_dists[0] returned from nearestKSearch().