Believe that v3 dirauths always serve extra infos.

Clients should always believe that v3 directory authorities serve
extra-info documents, regardless of whether their server descriptor
contains a "caches-extra-info" line or not.

Fixes part of #11683.
Edit 0.2.5.5-alpha changelog for terseness and grammar.
Re-wrap the 0.2.5.5-alpha changelog
changelog edits from wfn and yawning
Reflow 0.2.5.5-alpha changelog
Give 0.2.5.5-alpha a release date
Bump version to Tor 0.2.5.5-alpha-dev
Bump version in master to 0.2.6.0-alpha-dev
Merge remote-tracking branch 'karsten/bug11683'
Authorities also advertise caches-extra-info

(Whoops, thought I had committed this before)

Improvement to 11683 fix. Based on patch from Karsten.
Remove code for Windows CE support

As far as I know, nobody has used this in ages.  It would be a
pretty big surprise if it had worked.

Closes ticket 11446.
Thread support is now required

Long ago we supported systems where there was no support for
threads, or where the threading library was broken. We shouldn't
have do that any more: on every OS that matters, threads exist, and
the OS supports running threads across multiple CPUs.

This resolves tickets 9495 and 12439.  It's a prerequisite to making
our workqueue code work better, since sensible workqueue
implementations don't split across multiple processes.
logic mixup, noticed by alphawolf
Update a comment and undef an identifier

 * Trac #11452