Fixes bug 23106; bugfix on 0.2.4.8-alpha.

Fortunately, we only support big-endian and little-endian platforms,
and on both of those, hton*() and ntoh*() behave the same.  And if
we did start to support middle endian systems (haha, no), most of
_those_ have hton*(x) == ntoh*(x) too.

This fixes a compilation warning on windows.

Bug not in any released Tor.

 * CLOSES #17639.
 * ADDS new --key-expiration commandline option which prints when the
   signing key expires.

Since we start with desc_clean_since = 0, we should have been
starting with non-null desc_dirty_reason.

Fixes bug 22884; bugfix on 0.2.3.4-alpha when X-Desc-Gen-Reason was
added.

Patch from Vort; fixes bug 23081; bugfix on fd992dee in
0.2.1.16-rc when set_main_thread() was introduced.

See the changes file for a list of all the symptoms this bug has
been causing when running Tor as a Windows Service.

"ours" merge to avoid version bump.

"Ours merge" to avoid version bump.

One log statement was a warning and has been forgotten. It is triggered for a
successful attempt at introducting from a client.

It has been reported here:
https://lists.torproject.org/pipermail/tor-relays/2017-August/012689.html



Three other log_warn() statement changed to protocol warning because they are
errors that basically can come from the network and thus triggered by anyone.

Fixes #23078.

Signed-off-by: David Goulet <dgoulet@torproject.org>

"ours" merge to avoid version bump.