Added a writeFormat() method to Algorithm which must be called by the
write() method of derived classes.

2. Algorithm::load/save added (moved from StatModel)
3. copyrights updated; added copyright/licensing info for ffmpeg
4. some warnings from Xcode 6.x are fixed

- added test for loading legacy files
- added version to new written models
- fixed loading of several fields in some models
- added generation of new fields from old data

initial commit; ml has been refactored; it compiles and the tests run well; some other modules, apps and samples do not compile; to be fixed

This allows subclasses of CvBoost to override initial weights that
update_weights uses without duplicating its entire implementation.

amplement weidhting according to L. Bourdev and J. Brandt paper "Robust Object Detection Via Soft Cascade"

(Sometimes sample_data became bad because the buffer with its values was deallocated early).

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

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)