libavahi-client uses this one to schedule events immediately.
However, CoarseTimerEvent may be called too late, and cause timeouts.

Preparing for a variant of TimerEvent with coarse 1-second
granularity, but cheaper (with a timer wheel).

Similar to commits 1686f4e8 and
30a5dd26

These flags are output-only.

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

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.

Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

Avoid closing it twice.

Finally fixes the regression by commit c1f4f1fd.