Previously it just used /usr/bin/env/python, which would fail if we
only had a "python3" binary.

Fixes bug 40095; bugfix on 0.4.4.1-alpha.

This is based on @eighthave's templates, and the work we've been
doing to present a uniform testing environment.

Eventually this should be used by every one of our CI scripts.

Fixes conflicts due to code movement.

This fixes bug 40083, which was introduced in 9f31908a in
0.2.8.1-alpha.

Resolves conflicts:
	src/core/or/channel.c
        src/test/test_channel.c

This function once served to let circuits continue to be built over
version-1 link connections.  But such connections are long-obsolete,
and it's time to remove this check.

Closes #40081.

This is a defense-in-depth fix; closes 6198.

Frequently we want to do

    if (s) {
      memwipe(s, 0, sizeof(s));
      tor_free(s);
    }

and it's good to have a way to do this concisely.