zeroconf/ZeroconfBonjour: Fix compile errors resulting from "refactor to SocketEvent" and reenable bonjour for darwin build

Fixes Windows compatibility.

Replaces the static Duplicate() method.

To make things simpler, AllocatedString is now a non-template class.

release v0.22.4

The Google overlords require me to change to 29 or else I can't upload
new releases to Google Play.

 https://developer.android.com/distribute/best-practices/develop/target-sdk

Increasing the protocol version to 0.22.4 to allow clients to detect
this feature.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1038

Of course, it should do that!

I havn't yet figured out how to use Android's system CA certificates
with CURL/OpenSSL, so a temporary workaround is to disable verify_peer
by default.  The data MPD transfers isn't extremely important, so the
servers's authenticity isn't extremely important either.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1059