Tramp: handle non-standard file system like GPFS

Tramp: handle non-standard file system like GPFS

* doc/misc/tramp.texi (Frequently Asked Questions):
Explain tramp-use-file-attributes.

* lisp/net/tramp.el (tramp-use-file-attributes): New defcustom and
defsubst.
(tramp-skeleton-file-exists-p):
* lisp/net/tramp-adb.el (tramp-adb-handle-file-executable-p)
(tramp-adb-handle-file-readable-p):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-handle-file-executable-p)
(tramp-sudoedit-handle-file-readable-p)
(tramp-sudoedit-handle-file-writable-p): Use it.
* lisp/net/tramp-sh.el (tramp-sh-handle-file-executable-p)
(tramp-sh-handle-file-readable-p)
(tramp-sh-handle-file-writable-p): Use it.
(tramp-sh-handle-set-file-acl): Fix property name.