[ffmpeg] Bump version to 1.2.4 with applied patches
[ffmpeg] add forgotten build_xbmc_win32.sh
Readd commit 31bbc1a785010f9da899506b609af3bb18dc9779, it was removed in commit 97c0df3787b0994b01732cebb614b2f81fdfc1db by mistake

Commit-author: michaelni
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>