Already handled by dh-golang.

dh-golang defaults to /usr/bin and I've found no better way to install
to /usr/sbin.

pcidentd is no library, therefore ship only the binary.

This change handles the following build warning:

    unused substitution variable ${misc:Built-Using}

These are all (relevant) options I found to restrict this service.

we had already depended on dh-systemd, but not explicitly used it before

this makes us compatible with (among others) irc.fau.de again, albeit
slightly lying about the type userid (which no one really seems to care
about anyway)

RFC 1413 explicitly requires \r\n as line ending (EOL).

contrary to RFC1413, some IRC networks cannot handle special characters
in the ident response (e.g. '+' on freenode)

increase the length of sent response from 8 to 12 to make up for the
lost character range (of which many popular networks only use 10)

not even all freenode hosts have a reverse dns ending in .freenode.net,
some (quakenet..) often have none at all, so our heuristic is pretty
much useless