Fixed perf tests crash in case of corrupted sanity data; added option to control process of generating new sanity records

fixed crash in I/O tests on Windows by making sure std::vector is non-empty before taking pointer to its elements

reduced the video size in video writer tests; retained only most popular codecs. added ffmpeg support on MacOSX.

Libs for Android x86 added.

probably, ultimately fixed the problem of empty clusters in kmeans; added test for singular kmeans cases

Java tests fixes are expected shortly

make Mat::Mat(CvMat* m) return empty matrix when m is NULL; added utility Mat::initEmpty() method to replace duplicated matrix initializations in different constructors

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