OS X 10.5 provides a libutil in /usr/lib that is not the normal libutil.

Don't include it in LIBS if it doesn't actually contain the symboles we're
looking for.  Darwin's won't, LInux's will, so things will work out right.

This commit was SVN r19283.

configure.ac

@@ -738,7 +738,8 @@ AC_CACHE_SAVE
 
 ompi_show_title "Library and Function tests"
 
-AC_CHECK_LIB([util], [openpty])
+# Darwin doesn't need -lutil, as it's something other than this -lutil.
+OMPI_CHECK_FUNC_LIB([openpty], [util])
 
 AC_CHECK_LIB([nsl], [gethostbyname])