Implement EXCL of write-region for Tramp

Implement EXCL of write-region for Tramp

* lisp/net/ange-ftp.el (ange-ftp-write-region):
* lisp/net/tramp-adb.el (tramp-adb-handle-write-region)
* lisp/net/tramp-gvfs.el (tramp-gvfs-handle-write-region):
* lisp/net/tramp-sh.el (tramp-sh-handle-write-region)
* lisp/net/tramp-smb.el (tramp-smb-handle-write-region):
Implement MUSTBENEW.

* lisp/net/tramp-gvfs.el (tramp-gvfs-do-copy-or-rename-file)
* lisp/net/tramp-sh.el (tramp-sh-handle-make-symbolic-link)
(tramp-sh-handle-add-name-to-file)
(tramp-do-copy-or-rename-file)
* lisp/net/tramp-smb.el (tramp-smb-handle-make-symbolic-link):
Adapt error message for `file-already-exists'.

* src/lisp.h:
* src/eval.c (call8): New function.

* src/fileio.c (write_region): Pass also lockname and
mustbenew to the file name handler.

* test/lisp/net/tramp-tests.el (tramp-test10-write-region):
Add tests for MUSTBENEW.