* net/tramp-cache.el (tramp-get-hash-table): New defun.
(tramp-get-file-property, tramp-set-file-property)
(tramp-get-connection-property, tramp-set-connection-property): Use it.
(tramp-flush-file-property, tramp-flush-directory-property):
Rename argument to KEY.
(tramp-flush-connection-property): Simplify a little bit.
(tramp-connection-property-p): New defun.
(top): Reapply saved values only if there isn't a corresponding
entry in `tramp-connection-properties'.