Log Message:
tarsnap: update to 1.0.40.

Tarsnap 1.0.40 is now available.  This version brings several improvements
compared to tarsnap 1.0.39:

* tarsnap now accepts a --resume-extract option to skip extracting files whose
  filesize and mtime match existing files on disk.

* tarsnap now accepts --progress-bytes SIZE, which prints a progress message
  after each SIZE bytes are processed, up to once per file.  This can be
  disabled with --no-progress-bytes.

* tarsnap now accepts a --passphrase method:arg option which accepts:
  * --passphrase dev:tty-stdin
  * --passphrase dev:stdin-once
  * --passphrase dev:tty-once
  * --passphrase env:VARNAME
  * --passphrase file:FILENAME

* tarsnap now accepts a --dump-config option to print the command-line and all
    non-blank lines read from config files.

* tarsnap now exits with an error if there are unused command-line arguments.
  (i.e. "tarsnap -d -f a1 a2", where "a2" is unused.)

* Improved performance on some x86, amd64, and arm64 systems by using
  cryptographic instruction set extensions.

* When sent SIGINFO or SIGUSR1, tarsnap now prints the number of files and the
  number of uncompressed bytes processed, in addition to the previous output.

* A zsh completion file can be installed with
  configure --with-zsh-completion=DIR.

As usual, there are also lots of minor build fixes, harmless bug fixes, and
code cleanups.