Force the native libtool in Mac OS X to avoid GNU libtool [Beebe].

configure

@@ -231,7 +231,7 @@ if test "$gcc" -eq 1 && ($cc -c $cflags $test.c) >> configure.log 2>&1; then
              SHAREDLIBV=libz.$VER$shared_ext
              SHAREDLIBM=libz.$VER1$shared_ext
              LDSHARED=${LDSHARED-"$cc -dynamiclib -install_name $libdir/$SHAREDLIBM -compatibility_version $VER1 -current_version $VER3"}
-             AR="libtool"
+             AR="/usr/bin/libtool"
              ARFLAGS="-o" ;;
   *)             LDSHARED=${LDSHARED-"$cc -shared"} ;;
   esac