Warnings fix;

Added test checking that all valid fourcc values are converted properly

Сonflict exists between some versions of libtiff and opencv headers

OpenCV issue #2604

After this patch applied an attempt to encode empty images produces exception
saying "Raw image encoder error: Empty JPEG image (DNL not supported)"

disabled several tests on Mac when no FFMPEG is used; disabled automatic table initialization in imgwarp in the case of MinGW

get back to single-version ffmpeg wrapper (no more v2); make sure the library builds and the tests pass on Ubuntu 10.04 that includes pretty old version of ffmpeg

avoid simultanous reading data from 2 videos Highgui_Video.regression, since earlier versions of ffmpeg (or the way our wrapper uses them) can not handle that properly

Minor improvements: reduced verbosity of positioning tests; run.py - filter out non-executables on windows