Merge branch 'refs/heads/t/sha256'

A couple of changes which start to eliminate the use of sha1 in favor
of sha256. This series is only the first step, though, as we need to
keep sha1 for the time being to provide backward compatibility.

Cooking for four months.

* refs/heads/t/sha256:
  manual: Avoid sha1.
  upgrade_db: Add copyright and purpose to upgrade_db.c.
  web: Add link to the para_upgrade_db(1) man page.
  afs: Switch to sha256 and change default database path.
  Add para_upgrade_db.
  Use sha256 for the challenge response.
  Introduce hash2 (sha256).
  Assume sideband and aes_ctr128 are always supported/requested.

diff --cc Makefile.in
Simple merge

diff --cc Makefile.real
Simple merge

diff --cc NEWS.md
index a31aeaf18e04b32b496f47cea04988fd74f5536f,3e3e7abfda28365cba7abfa2ead1c2c408d75801..9e67364d9d6c2bb4dd8390e4a5ee5a524bbe5157
--- 1/NEWS.md
--- 2/NEWS.md
+++ b/NEWS.md
@@@ -1,65 -1,6 +1,80 @@@
  NEWS
  ====
  
 +---------------------------------------
 +0.7.0 (to be announced) "seismic orbit"
 +---------------------------------------
 +
++- Starting with paraslash-0.7.0, the sha256 hash value of each known
++  audio file is stored in the database while older versions employed the
++  sha1 hash algorithm which has been considered insecure since 2005
++  and should no longer be used today. The switch from sha1 to sha256
++  requires users to upgrade their database using the new para_upgrade_db
++  program, followed by re-adding all files to recompute the hashes. With
++  this approach all metadata stored in the database (last played date,
++  num played value, moods, playlists, attributes etc.) are kept. An
++  simpler alternative is to start over from scratch by running the
++  "init" command but this will lose these metadata.
++- Server and client now hash the session keys with sha256 rather
++  than sha1 during the initial handshake. This feature is optional and
++  backwards compatible: old clients can still connect to a new server
++  (using sha1). Also new clients can connect to an old server (again
++  using sha1).
 +- The new "duration" keyword of the mood grammar makes it possible to
 +  impose a constraint on the duration of the admissible files.
 +- The long deprecated version 1 mood syntax is no longer supported.
 +- Paraslash writers handle early end-of-file more gracefully.
 +- The alsa writer no longer warns about spurious underruns.
 +- The score formula  of the audio file selector has been reworked.
 +- Cleanups of the doubly linked lists code.
 +- New option for configure: --enable-ubsan to detect and report undefined
 +  behaviour.
 +- The "tasks" server command has been removed.
 +
 +Downloads:
 +[tarball](./releases/paraslash-git.tar.xz)
 +
 +--------------------------------------
 +0.6.4 (2021-11-04) "fuzzy calibration"
 +--------------------------------------
 +
 +This point release contains a fair number of fixes but no new features.
 +This marks the end of the 0.6 development, although paraslash-0.6 will
 +still be supported for some time and subsequent maintenance releases
 +may follow.
 +
 +- The udp sender no longer crashes when empty chunks are encountered.
 +- Fix a double-free bug in the exit path of the server.
 +- The "jmp" command now errors out when given a negative percentage.
 +- A fix for a bug in para_afh which triggered on the attempt to modify
 +  the tags of an invalid mp4 file.
 +- A memory leak in para_afh has been fixed.
 +- The udp sender no longer sends multiple EOF packets.
 +- Some gcc warnings have been silenced.
 +- Minor log level adjustments and documentation improvements.
 +
 +Downloads:
 +[tarball](./releases/paraslash-0.6.4.tar.xz),
 +[signature](./releases/paraslash-0.6.4.tar.xz.asc)
 +
 +---------------------------------------
 +0.5.9 (2021-11-04) "reversed dimension"
 +---------------------------------------
 +
 +This release contains a few important fixes which have accumulated in
 +the maint branch. The paraslash-0.5.x series has now reached its end
 +of life and will no longer be supported. All users should upgrade to
 +a more recent version at this point.
 +
 +- Fix an issue with the bash completion script.
 +- Initialize the random seed also when using libgrypt.
 +- Fix some compiler warnings in the resample filter
 +- Don't return spurious errors from the ff server command.
 +
 +Downloads:
 +[tarball](./releases/paraslash-0.5.9.tar.bz2),
 +[signature](./releases/paraslash-0.5.9.tar.bz2.asc)
 +
  ----------------------------------------
  0.6.3 (2021-02-18) "generalized activity"
  -----------------------------------------

diff --cc afs.c
Simple merge

diff --cc command.c
Simple merge

diff --cc configure.ac
Simple merge

diff --cc web/documentation.in.html
index e1587afbfe3bd9a0a9c3c10a2d32657794633dc2,e863e7b9faa45c4a895355377694c493d5512e5d..8e85f7fc5b260b73b095cbea04f7ff7a72fb2017
--- 1/web/documentation.in.html
--- 2/web/documentation.in.html
+++ b/web/documentation.in.html
@@@ -23,8 -23,9 +23,9 @@@
        [<a href="para_filter.man.html">para_filter</a>]
        [<a href="para_write.man.html">para_write</a>]
        [<a href="para_gui.man.html">para_gui</a>]
 -      [<a href="para_mixer.man.html">para_mixere</a>]
 +      [<a href="para_mixer.man.html">para_mixer</a>]
        [<a href="para_play.man.html">para_play</a>]
+       [<a href="para_upgrade_db.man.html">para_upgrade_db</a>]
  </p>
  
  <h2> Source code documentation </h2>

diff --cc web/manual.md
Simple merge