possibly fixed crash boost caused by the recent modification; slightly improved mlp params in letter_recog sample

Documentation: fixed class/struc members documentation; added warning on incorrectly documented member

fixed 2 build problems on MacOSX (highgui with ffmpeg, opencv_world); added macro CV_INIT_ALGORITHM for simpler algorithm registration (ticket #1876)

added opencv_world module that combines all the other [selected by user] OpenCV modules, except for opencv_python and opencv_gpu.

fixed potential buffer size overflow in Boost::update_weight, bug #1524 (thanks to benlemna for the patch)

 [~] Automatically tracked dependencies between modules
 [+] Support for optional module dependencies
 [+] Options to choose modules to build
 [~] Removed hardcoded modules lists from OpenCVConfig.cmake, opencv.pc and OpenCV.mk
 [+] Added COMPONENTS support for FIND_PACKAGE(OpenCV)
 [~] haartraining and traincascade are moved outside of modules folder since they aren't the modules