(HAVE_RES_INIT): Define if res_init() exists.

(HAVE_LIBRESOLV): Also define if we are using res_init().

configure.in

@@ -2731,7 +2731,7 @@ AC_CHECK_HEADERS(maillock.h)
 
 AC_CHECK_FUNCS(gethostname getdomainname dup2 \
 rename closedir mkdir rmdir sysinfo getrusage get_current_dir_name \
-random lrand48 bcopy bcmp logb frexp fmod rint cbrt ftime res_init setsid \
+random lrand48 bcopy bcmp logb frexp fmod rint cbrt ftime setsid \
 strerror fpathconf select mktime euidaccess getpagesize tzset setlocale \
 utimes setrlimit setpgid getcwd getwd shutdown getaddrinfo \
 __fpending mblen mbrlen mbsinit strsignal setitimer ualarm index rindex \
@@ -2775,17 +2775,38 @@ AC_CHECK_FUNCS(getpt)
 # than to expect to find it in ncurses.
 AC_CHECK_LIB(ncurses, tparm)
 
+# Do we have res_init, for detecting changes in /etc/resolv.conf?
+
+resolv=no
+AC_CHECK_FUNC(res_init, have_res_init=yes, have_res_init=no)
+if test "$have_res_init" = no; then
+  OLIBS="$LIBS"
+  LIBS="$LIBS -lresolv"
+  AC_MSG_CHECKING(for res_init with -lresolv)
+  AC_TRY_LINK([#include <netinet/in.h>
+#include <arpa/nameser.h>
+#include <resolv.h> ],
+    [res_init();],
+    have_res_init=yes, have_res_init=no)
+  AC_MSG_RESULT($have_res_init)
+  if test "$have_res_init" = yes ; then
+    resolv=yes
+  fi
+  LIBS="$OLIBS"
+fi
+
+if test "$have_res_init" = yes; then
+  AC_DEFINE(HAVE_RES_INIT, 1, [Define to 1 if res_init is available.])
+fi
+
 # Do we need the Hesiod library to provide the support routines?
 if test "$with_hesiod" = yes ; then
   # Don't set $LIBS here -- see comments above.
-  resolv=no
   AC_CHECK_FUNC(res_send, , [AC_CHECK_FUNC(__res_send, ,
      [AC_CHECK_LIB(resolv, res_send, resolv=yes,
 		  [AC_CHECK_LIB(resolv, __res_send, resolv=yes)])])])
   if test "$resolv" = yes ; then
     RESOLVLIB=-lresolv
-    AC_DEFINE(HAVE_LIBRESOLV, 1,
-	      [Define to 1 if you have the resolv library (-lresolv).])
   else
     RESOLVLIB=
   fi
@@ -2795,6 +2816,12 @@ if test "$with_hesiod" = yes ; then
 	:, $RESOLVLIB)])
 fi
 
+# Do we need libresolv (due to res_init or Hesiod)?
+if test "$resolv" = yes ; then
+  AC_DEFINE(HAVE_LIBRESOLV, 1,
+            [Define to 1 if you have the resolv library (-lresolv).])
+fi
+
 # These tell us which Kerberos-related libraries to use.
 if test "${with_kerberos+set}" = set; then
   AC_CHECK_LIB(com_err, com_err)