avutil/utils: check and warn about llrint() brokenness

Such broken llrint() exist for example on netbsd

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/vc1dec: Check source picture availability in vc1_mc_4mv_chroma4()

Fixes null pointer dereference

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Document "cache" protocol

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavu/hash: Add support for SHA-2 512

Signed-off-by: James Almer <jamrial@gmail.com>
lavf/md5enc: Use AV_HASH_MAX_SIZE

Also increase the buffer size in write_trailer(), since 128
is not enough anymore

Signed-off-by: James Almer <jamrial@gmail.com>
lavu: Add RIPEMD hashing

Includes RIPEMD-128, RIPEMD-160, RIPEMD-256 and RIPEMD-320

Signed-off-by: James Almer <jamrial@gmail.com>