If it's followed by a slash and OpenCV_INSTALL_BINARIES_PREFIX is empty,
then the resulting path becomes absolute.

Fixes <http://code.opencv.org/issues/3350>.

FFmpeg 2.0.2 32-bit builded with mingw (4.6.1) with following additional options: --enable-w32threads --disable-iconv --cpu=i686 (workaroud for http://trac.ffmpeg.org/ticket/2363)

Also fixed some typos and code alignment
Also adapted tutorial CPP samples
Fixed some identation problems

The general convention is <output file name> + ".in".

avformat_find_stream_info was introduced in Libav avformat 53.3,
but it was only merged to FFmpeg in avformat 53.6.

In Libav avformat 53.3-53.5 av_find_stream_info is not removed
(only deprecated), so this shouldn't break building with that.