http-support.c: Add avahi-common/malloc.h header for avahi_free()
#elif defined(HAVE_AVAHI)
# include <avahi-client/client.h>
# include <avahi-client/lookup.h>
+# include <avahi-common/malloc.h>
# include <avahi-common/simple-watch.h>
#endif /* HAVE_DNSSD */
