Previously the result was returned as the exit code of the function
(which would prevent the usage of "set -e").
Additionally the fallback value that was previously calculated outside
of the function is now part of it.
Previously (before the multigraph conversion) the configuration setting
for "lxc_ram" was called "areastack". The multigraph conversion
documented a new configuration setting "ram_areastack", but it was not
used, yet.
Thus we can switch to a more descriptive name: "ram_display_stacked".
