Frontal cat face detectors

This commit adds Haar and LBP detectors for frontal cat faces.  See the comments at the top of the cascade files.  A detailed tutorial on training these detectors is included in my upcoming book, OpenCV for Secret Agents (Packt Publishing, January 2015).  Here are screenshots of the detectors in action:

![7376os_03_01](https://cloud.githubusercontent.com/assets/376134/5559958/b606c78a-8d3c-11e4-99a6-45a4e56b6c41.png)
![7376os_03_xx](https://cloud.githubusercontent.com/assets/376134/5559972/32ce913a-8d3d-11e4-8ad0-abdd1eab1b3d.png)

I am also addressing some (unrelated) const correctness problems in cap_openni.cpp and cap_openni2.cpp.  These issues were introduced by commit 61886a61de82ef5e837b1f3d163f4666ea16a2da ("Merge pull request #3504 from a-wi:VideoCapture_get_const_v3") and were preventing the buildbot from building on Linux x64.