DCP: read encrypted DCP with KDM files

Uses libgcrypt

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
contrib: Set pkg-config path in ffmpeg configure

Although we know in the contrib build system the path to pkg-config,
ffmpeg does not always pick it up and dependency resolution will
fail.

Acked-by: Rémi Denis-Courmont <remi@remlab.net>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
UNPACK_DIR should only strip .tar as 2nd suffix

Fixes the problem where UNPACK_DIR returned rtmpdump-2 instead
of rtmpdumo-2.3 for rtmpdump-2.3. Only .tar.* archives have two
filetype suffixes, tgz, zip,.. have only one and the second "."
in the filename belongs to the version number which should not be
stripped.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>