This adds support for input samples other than 16 bit to the FFmpeg
filter plugin.

If no conversion is necessary, return the child Filter as-is.  This
allows removing all nullptr checks from AutoConvertFilter.

If the FFmpeg filter outputs planar data, interleave it, just like the
FFmpeg decoder plugin does.

To be reused by the FFmpeg filter plugin.

This compatibility macro has been removed from FFmpeg long ago.

filter_chain_parse() passes a temporary string pointer which results
in a use-after-free in the PreparedChainFilter::Child::Open() error
message.

This allows users to disable the "CUE files as directories" feature
without having to disable the CUE playlist plugin completely.  This
feature has been annoying some users.

It's been 9 years already, and there's no point in insisting on the 21
year old C standard.  MPD doesn't have a lot of C code left, but why
not compile it with the latest language revision.

Since MPD is a long-running daemon, it doesn't make sense to use
dynamic binding.  That allows the relocations to be read-only
("relro"), which a hardening feature.

The latter creates a new object, but we know that the key already
exists.

The latter creates a new object, but we know that the key already
exists.

This allow using erase() with iterator, without a key lookup.

Found with readability-use-anyofallof
Signed-off-by: Rosen Penev <rosenp@gmail.com>

release v0.22.2