silent compiling warnings for VC9 build

libmkv/EbmlWriter.c

nestegg/src/nestegg.c

vp8/decoder/dboolhuff.h

vp8/decoder/decodframe.c

vp8/encoder/bitstream.c

vp8/encoder/denoising.c

vp8/encoder/encodeframe.c

vp8/encoder/firstpass.c

vp8/encoder/onyx_if.c

vp8/encoder/onyx_int.h

vp8/encoder/ratectrl.c

vp8/vp8_cx_iface.c

vpx_ports/x86.h

vpxdec.c

vpxenc.c

y4minput.c