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

replaced alloca() (a.k.a. cvStackAlloc) with AutoBuffer or vector() everywhere. cvStackAlloc() is still defined, but we do not need alloca() anymore to compile and run OpenCV (fixes #889 and may be some others)

added more helper macros to the function declarations, to assist the Python wrapper generator. Fixed memleak in Mat::operator()(Range,Range) and the related functions (Mat::row, Mat::col etc.)