Swap/undo/backup is working again

Swap/undo/backup is working again

Not sure, but sometime after the end of April the whole swap/undo/backup
stuff quit working.  It's almost as if a system configuration file
changed, but I don't know what.  In any case, the changes here to vimrc
(~/.vimrc) gets things working even better:

* If the directory structure used for these files, at
  ~/.local/share/vim, are not present, they are created.
* If backups can be written, only the preferred location is made
  available.
* If undo files can be written, only the preferred location is made
  available.