bug#23865: 24.5; doc string of `tramp-remote-path'

[Drew Adams]

> The docstring of `tramp-remote-path' is oriented to the custom
> interface. In custom, `tramp-default-remote-path' and
> `tramp-own-remote-path' are not offered under their symbol name, but as
> "Default Directories" and "Private Directories". These entries are
> documented.

Right.  That's the (doc) bug.  It is fine to be "oriented" to
interactive use of Customize.  It is a failing to incorrectly
describe the variable value.  That hurts, rather than helps
users.  The doc string can do both: describe things in terms
of the UI and also correctly describe the possible values.

What it should not do is what it does now: give the impression
that the list values are all strings (and not say anything
about those two symbols that have special meaning for the
variable value).