Sync with Tramp 2.6.3-pre (don't merge with master)

Sync with Tramp 2.6.3-pre (don't merge with master)

* doc/misc/tramp.texi (Obtaining @value{tramp}): Mention the ELPA
Tramp manual.
(Remote processes): Adapt index.

* doc/misc/trampver.texi:
* lisp/net/trampver.el (tramp-version): Set to "2.6.3-pre".

* lisp/net/tramp.el (tramp-local-host-regexp): Extend.  Adapt :version.
(tramp-signal-process): PROCESS can also be a string.
(tramp-skeleton-directory-files):
* lisp/net/tramp-cache.el (with-tramp-saved-file-property)
(with-tramp-saved-file-properties)
(with-tramp-saved-connection-property)
(with-tramp-saved-connection-properties): Use `setf' but `setq' in macro.

* lisp/net/tramp-compat.el (tramp-compat-funcall): Declare debug.

* lisp/net/tramp-crypt.el (tramp-crypt-file-name-p): Exclude lock files.
(tramp-crypt-file-name-handler-alist): Use `identity' for
`abbreviate-file-name'.
(tramp-crypt-add-directory, tramp-crypt-remove-directory):
Adapt docstrings.
(tramp-crypt-cleanup-connection): New defun.  Add it to
`tramp-cleanup-connection-hook'

* lisp/net/tramp.el (tramp-skeleton-file-name-all-completions):
Handle "." and "..".

* lisp/net/tramp-adb.el (tramp-adb-handle-file-name-all-completions):
* lisp/net/tramp-fuse.el (tramp-fuse-handle-file-name-all-completions):
* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-file-name-all-completions):
Remove special handling of "." an "..".

* lisp/net/tramp-sh.el (tramp-pipe-stty-settings): New defcustom.
(tramp-sh-handle-make-process): Use it.  (Bug#62093)

* test/lisp/net/tramp-tests.el (tramp-test18-file-attributes):
Adapt test.
(tramp-test31-signal-process): Extend.