"Ours" to avoid version bump.

"ours" merge to avoid version bump

"ours" merge to avoid cherry-picked copy of #25512 fix, which is already in
this branch.

Fixes bug 25512.

(Cherry-picked from 3519d0c8

It's needed by main.c

Fixes bug 26662; bug not in any released Tor.

I am very glad to have written this script.

This commit won't build yet -- it just puts everything in a slightly
more logical place.

The reasoning here is that "src/core" will hold the stuff that every (or
nearly every) tor instance will need in order to do onion routing.
Other features (including some necessary ones) will live in
"src/feature".  The "src/app" directory will hold the stuff needed
to have Tor be an application you can actually run.

This commit DOES NOT refactor the former contents of src/or into a
logical set of acyclic libraries, or change any code at all.  That
will have to come in the future.

We will continue to move things around and split them in the future,
but I hope this lays a reasonable groundwork for doing so.

This is a very gentle commit that just lays the groundwork in the
build system: it puts the include files to build libtor-app.a into
src/core, and to build the tor executable into src/app.  The
executable is now "src/app/tor".