Closes https://github.com/MusicPlayerDaemon/MPD/issues/1156

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

For efficient traversal within one partition, e.g. for distributing
partition-local idle events.

Caused by a revert accident in commit
f2cdbeac

Closes https://github.com/MusicPlayerDaemon/MPD/issues/631

libwrap is an obscure artefact from a past long ago, when source IP
address meant something.

And its API is "interesting"; it requires the application to expose
two global variables `allow_severity` and `deny_severity`.  This led
to bug #437.  I don't want to declare those variables; instead, I'd
like to remove libwrap support.

Closes #437

Prepare for per-listener permissions.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

Passing it by value is actually smaller (32 bit) than the rvalue
reference (64 bit pointer), and it ensures that the object is consumed
after the call returns, no matter how the methods are implemented.

Prepare to make it mutable.

Prepare to convert "partition" to a mutable pointer.