added documentation for ORB (ticket #1835). updated documentation on features2d (Feature2D class is still to be documented) (ticket #1819)

put template Distance classes back to features2d, since they are used in GPU; fixed OpenCV build with Xcode 2.3 (which includes new libpng)

added BruteForceMatcher (the older variant of BFMatcher) to legacy (ticket #1796). added test for it. Renamed legacy tests to "Legacy_*"

added dedicated <modname>_init.cpp files with initModule_<modname>() functions and all the relevant structures; made BackgroundSubtractorMOG/MOG2 derivatives from Algorithm; cleaned up MOG2 implementation and made it multi-threaded.

Suppressed hundreds of useless MSVC warnings (can be reenabled setting cmake variable ENABLE_NOISY_WARNINGS to ON). Fixed some of remaining warnings.

added initModule_features2d(). Possibly solved problem when the linker excludes seemingly unused detectors/descriptors.

Made small change which fixes the situation, when ORB does not find any descriptors on an image. Earlier ORB::operator() crashed in this case, since rowRange method was called for an empty matrix.

lot's of changes; nonfree & photo modules added; SIFT & SURF -> nonfree module; Inpainting -> photo; refactored features2d (ORB is still failing tests), optimized brute-force matcher and made it non-template.

minor build system changes (now cuda code in opencv_core is compiled using CUDA_ARCH* cmake variables)

 [~] 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

Refactored performance tests. TEST_CYCLE macro is renamed to TEST_CYCLE_N; SIMPLE_TEST_CYCLE is renamed to TEST_CYCLE; from now 100 iterations are default for performance tests

updated ORB: limit the number of output keypoints, use bi-linear interpolation between subsequent layers instead of much slower area-based interpolation between 0-th and i-th layers.