Fix for the libltdl preopen commit. So now autogen will progress without emiting an error.

{{{
grep: configure: No such file or directory
./autogen.sh: line 495: config/libltdl-preopen-error.patch: No such file or directory
}}}

This commit was SVN r22823.

autogen.sh

@@ -492,7 +492,7 @@ EOF
         fi
         echo "   ++ preopen error masking ib libltdl"
         if test -r opal/libltdl/loaders/preopen.c; then
-            patch -N -p0 < config/libltdl-preopen-error.patch
+            patch -N -p0 < config/libltdl-preopen-error.diff
             rm -f opal/libltdl/loaders/preopen.c.rej
         fi