gracefully handle file operation errors for load/save
[ This was originally reported by chrysn-guest on 2014-12-12 13:22 as issue 314907 on alioth. ]
in situations with no user writable user account or ~/.screenlayout directory, appropriate error handling should be implemented.
in no case should file permissions be touched (even umask should be relied on unmodified), but errors resulting from weird permissions should at least be indicated to the user.
Edited by chrysn