Replace full-path restart links with relative links (#1816)

Symlinks for the final restart time used the full path name, even
though the targets are in the same directory. This means the links
would break if the directory were moved or (more importantly) put
in a tarball. The links have now been replaced with relative links.

Resolves #1446

ush/forecast_predet.sh

@@ -210,7 +210,7 @@ FV3_predet(){
       done
     done
     for file in ${files}; do
-      ${NLN} "${COM_ATMOS_RESTART}/${file}" "${COM_ATMOS_RESTART}/${forecast_end_cycle:0:8}.${forecast_end_cycle:8:2}0000.${file}"
+      ${NLN} "${file}" "${COM_ATMOS_RESTART}/${forecast_end_cycle:0:8}.${forecast_end_cycle:8:2}0000.${file}"
     done
   else
     mkdir -p "${DATA}/RESTART"