vf_lut: make config_props work properly when called multiple times.

Do not leak the expressions.
vf_gradfun: make config_props work properly when called multiple times.
vf_frei0r: make config_props work properly when called multiple times.

Do not leak the initialized filter instance.
vf_fps: move initializing pts from config_props to init.

It should not be reinitialized if the link properties change.
vf_drawtext: do not reset the frame number in config_input.

Frame number should be incremented normally even if the link properties
change.
vf_drawbox: make config_props work properly when called multiple times.

Do not overwrite the variables set through AVOptions.
vf_setdar: make config_props work properly when called multiple times.

Do not overwrite the variable set through AVOptions.
vf_crop: make config_props work properly when called multiple times.

Do not leak the x/y expressions.
vf_drawtext: don't leak the expressions.
vf_hqdn3d: make config_props work properly when called multiple times.

Do not leak all the temp buffers.
vf_pixdesctest: make config_props work properly when called multiple times.
lavc/pthread: remove obsolete checks

Those were useful when avcodec_thread_init() was a public functions. It
was deprecated and removed some time ago, so those checks are not needed
anymore.
pthread: reindent
mpegvideo: allocate sufficiently large scratch buffer for interlaced vid

MPV_decode_mb_internal needs 3 * 16 * linesize bytes of scratch buffer

For interlaced content, linesize is multiplied by two after the allocation
of the scratch buffer, and the dest_cr pointer ends past the buffer.

This patch makes ff_mpv_frame_size_alloc allocate a total of
(aligned line_size) * 2 * 16 * 3 bytes, which suffices even for the
interlaced case.

CC:libav-stable@libav.org

Signed-off-by: Jindrich Makovicka <makovick@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>