libink: trace connections, calls, and authorization decisions

The legacy socket logs a line per command under initctl debug; the bus
logged nothing, so the transport that now carries most of initctl was
the one you could not watch.

libink gets a logger hook rather than a dependency on Finit's: it
passes the emitting function and a formatted message, and dbus.c hands
both to logit() so the two sources read alike.  Trace points cover the
connection lifecycle, every inbound call, and why a call was refused.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

libink/Makefile.am

@@ -11,7 +11,7 @@ libink_la_SOURCES        = server.c auth.c connection.c \
                            dispatch.c builtin.c          \
                            match.c                       \
                            path.c                        \
-                           client.c io.c                 \
+                           client.c io.c log.c           \
                            link.h path.h internal.h
 
 libink_la_CPPFLAGS       = -D_GNU_SOURCE -D_DEFAULT_SOURCE -D_BSD_SOURCE