Add `slow' and `history' tags to the desktop data.

Add `slow' and `history' tags to the desktop data.

* info.el (Info-virtual-nodes) [*Index*]: Add `slow' tag.
(Info-virtual-files) [*Apropos*]: Add `slow' tag.
(Info-finder-find-node): Require `finder.el' to be able
to restore node from the desktop.
(Info-desktop-buffer-misc-data): Save all nodes.  Save additional
data `Info-history' and `slow' tag in the assoc list.
(Info-restore-desktop-buffer): Don't restore nodes with the
`slow' tag.  Restore `Info-history'.