Added const modifiers to OctreePointCloud function

- Added const keyword to function 'OctreePointCloud::getVoxelBounds ()',
  since it internally only calls a 'const' function
  ('OctreePointCloud::genVoxelBoundsFromOctreeKey ()')
- Added const modifier to 'OctreeIterator' input argument of
  'OctreePointCloud::getVoxelBounds ()', since only 'const' functions
  of 'OctreeIterator' are called
Merge pull request #1016 from SvenAlbrecht/octree_const_mods

Added const modifiers to OctreePointCloud function
Fix ImageViewer in VTK 6.1
Merge pull request #1017 from VictorLamoine/vtk6_fixes

Fix ImageViewer in VTK 6.1
Fix Eigen error
Merge pull request #1019 from VictorLamoine/renderView_fix

Fix Eigen error
further fix for issue #1012 when compiling on Windows 32bit (MSVC2010). If class BearingAngleImage is exported using PCL_EXPORTS, its base class pcl::PointCloud must be exported as well.
Merge pull request #1020 from magro11/PCL_EXPORTS_pointCloud

further fix for issue #1012 when compiling on Windows 32bit (MSVC2010). ...
Fix: invalid array allocation in iss_3d.hpp

If OPENMP is not used, the variable threads_ is zero by default. Thus
the array allocation

   Eigen::Vector3d *omp_mem = new Eigen::Vector3d[threads_];

leads to a valid but zero sized array and finally to an invalid write
at line 381-383 (375-377).
Merge pull request #1022 from jgarstka/iss_3d_bugfix

Fix: invalid array allocation in iss_3d.hpp
correct the mistakes in pcl::visualiztion::renderView
First, "world_coords[3]" should be set to 1.0f before transformation.
Second, "-y, -x" operations should be applied after "mat2".