Eigen with std::vector fixes

[VictorLamoine]

Fixes #958

$ grep "std::vector<Eigen" -rn /home/$USER/pcl | grep -vw 'aligned_allocator'
/home/victor/pcl/recognition/include/pcl/recognition/face_detection/rf_face_detector_trainer.h:230:      void getDetectedFaces(std::vector<Eigen::VectorXf> & faces)
/home/victor/pcl/apps/include/pcl/apps/face_detection/face_detection_apps_utils.h:112:  void displayHeads(std::vector<Eigen::VectorXf> & heads, pcl::visualization::PCLVisualizer & vis)
/home/victor/pcl/apps/src/face_detection/openni_face_detection.cpp:70:    std::vector<Eigen::VectorXf> heads;
/home/victor/pcl/apps/src/face_detection/filesystem_face_detection.cpp:85:  std::vector<Eigen::VectorXf> heads;

These are fine: http://eigen.tuxfamily.org/dox/group__TopicFixedSizeVectorizable.html

[VictorLamoine]

Building is ok on my side

[taketwo]

Hi Victor, thanks for the effort. Unfortunately I've been quite busy lately and do not have enough time to go through all the piled up requests. But I'll have a look asap.

[VictorLamoine]

We are not in a hurry; take your time!

[jspricke]

I had a quick look, and as it seems to be more or less automatically generated, I would merge it tomorrow, if no one objects.

[taketwo]

+1