State across application invocation

[Soeren Sandmann <sandmann daimi au dk>]

This has been brought up and shot down before, but now I'm bringing it
up again. Applications sometimes need a way to make parts of their
state persistent across invocations. Examples:

        * The most obvious example is a "recent documents"
          list. Applications need to store that list somewhere they
          can find it againg, and the list would ideally be global so
          that when you open a document in an instance of gnumeric,
          all other running instances of gnumeric would update their
          list.

        * Recent locations in nautilus is sort of the same thing, but
          with the additional twist that the information might be
          useful outside nautilus, eg in a URL launcher on the panel.

        * A news program needs to save the list of subscribed
          newsgroups.

        * A chat program might want to save the list of servers and
          channels that the user is connected to, so that it can
          suggest the same servers and channels the next time it
          starts.

To do this we need persistency and notifications, which is something
GConf can do. The only reason GConf currently can't be used for this
kind of data is that it isn't guaranteed to be writable. So I suggest
extending the gconf database with a location that is guaranteed to be
writable - sort of a dot-file with notifications.