multiple definition of cap_ffmpeg_impl.hpp functions in gpu and highgui

another fix to make OpenCV more friendly for iOS developers. We now use libc++ instead of libstdc++ and clang instead of gcc to build opencv2.framework.

Memory leak in color-blob-detection sample fixed;
Default face size in face-detection is set to 20%;
Error handling improved;
Some possible mat leak fixed;
Manager verison and engine interface version incremented to fix incompatibilities;
Docs updated;