make zlib.h a required header, not an optional header

svn:r2406

configure.in

@@ -139,11 +139,11 @@ LIBS="$saved_LIBS -lssl -lcrypto"
 
 dnl The warning message here is no longer strictly accurate.
 
-AC_CHECK_HEADERS(unistd.h string.h signal.h netdb.h ctype.h poll.h sys/stat.h sys/poll.h sys/types.h fcntl.h sys/fcntl.h sys/ioctl.h sys/socket.h sys/time.h netinet/in.h arpa/inet.h errno.h assert.h time.h pwd.h grp.h, , AC_MSG_WARN(some headers were not found, compilation may fail))
+AC_CHECK_HEADERS(unistd.h string.h signal.h netdb.h ctype.h poll.h sys/stat.h sys/poll.h sys/types.h fcntl.h sys/fcntl.h sys/ioctl.h sys/socket.h sys/time.h netinet/in.h arpa/inet.h errno.h assert.h time.h pwd.h grp.h zlib.h, , AC_MSG_WARN(some headers were not found, compilation may fail))
 
 dnl These headers are not essential
 
-AC_CHECK_HEADERS(stdint.h sys/types.h inttypes.h sys/param.h sys/wait.h sys/limits.h netinet/in.h arpa/inet.h machine/limits.h zlib.h)
+AC_CHECK_HEADERS(stdint.h sys/types.h inttypes.h sys/param.h sys/wait.h sys/limits.h netinet/in.h arpa/inet.h machine/limits.h)
 
 AC_CHECK_FUNCS(gettimeofday ftime socketpair uname inet_aton strptime)
 AC_REPLACE_FUNCS(strlcat strlcpy)