Fix a bug in RegionGrowing with oversized output cluster vector.

The clusters vector output by RegionGrowing<PointT, NormalT>::extract()
function was not properly trimmed after filtering out clusters that are
too small and too large. As a result many dozens/hundreds of zero-sized
clusters seeped into the output vector.
Added vtkPolyLine.h header to example_supervoxels.cpp

In 1.7.0 the supervoxel example doesn't build with Visual Studio 2012 (and others: https://github.com/PointCloudLibrary/pcl/issues/202).
Only build pcd_select_object_plane.cpp when QHull is available

As pcd_select_object_plane.cpp requires QHull it should be excluded when QHull is not found.
Check to only build in_hand_scanner when OpenNI is available
Switched from gl.h to qgl.h
Merge pull request #211 from henningpohl/patch-6

Switching from gl.h to qgl.h
Merge pull request #208 from henningpohl/patch-3

Check to only build in_hand_scanner when OpenNI is available
Merge pull request #207 from henningpohl/patch-2

Only build pcd_select_object_plane.cpp when QHull is available
Merge pull request #206 from henningpohl/patch-1

Added vtkPolyLine.h header to example_supervoxels.cpp
Merge pull request #205 from taketwo/region-growing-fix

Fix a bug in RegionGrowing with oversized output cluster vector.
Removed compiler options resulting in a D8021 compiler error in Visual Studio 2012
Merge pull request #214 from henningpohl/patch-1

Removed compiler options resulting in a D8021 compiler error in Visual Studio 2012