Backport Tramp changes from trunk.

* tramp.texi (Inline methods): Remove restriction on "telnet".
Recommend sharing ssh connections for "plink".
(External methods): Remove "sftp".  Merge "pscp" and "psftp"
descriptions.  Recommend sharing ssh connections.  Add "nc" method.
(GVFS based methods): Add "sftp".
(Customizing Completion, External packages, Issues): Use @dots{}.
(Remote shell setup): Explain, how to change command line
arguments of remote "nc" listener.

* trampver.texi: Update release number.