Problem in 4PCS implementation

1. at https://github.com/PointCloudLibrary/pcl/blob/master/registration/include/pcl/registration/ia_fpcs.h#L97
   typedef std::vector <MatchingCandidate> MatchingCandidates;
   Currently an assert is triggered inside Eigen when the vector allocates storage. MatchingCandidate contains an Eigen::Matrix4f member, which must be aligned at a 16-byte boundary. The fix is to use Eigen::aligned_allocator for the vector:
   typedef std::vector <MatchingCandidate, Eigen::aligned_allocator<MatchingCandidate> > MatchingCandidates;
   For details see http://eigen.tuxfamily.org/dox-devel/group__TopicStlContainers.html

2. at https://github.com/PointCloudLibrary/pcl/blob/master/registration/include/pcl/registration/impl/ia_fpcs.hpp#L181
   `#ifdef _OPENMP

   pragma omp flush (abort)

   endif

   MatchingCandidates candidates (1);`
   Although this is valid, a compiler bug in VC++ 2015 will prevent compilation with OpenMP enabled:
   https://stackoverflow.com/questions/35568653/why-doesnt-this-compile-vc-2015-pragma-omp-flush
   A solution (other than waiting till Microsoft fix their broken compiler) would be to add a semicolon below the #pragma and above the declaration, with a comment indicating its purpose.

Start at registration/include/pcl/registration/ia_fpcs.h around line 97 and registration/include/pcl/registration/impl/ia_fpcs.hpp around line 181. Review the Eigen alignment requirement and the VC++ 2015 OpenMP pragma behavior described in the issue. Done means the MatchingCandidates vector uses aligned allocation and the affected code compiles with OpenMP enabled on VC++ 2015.