This catches lines within command lists as well.

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

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Closes #296

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.