Unit tests for the 10 valid combinations of set/NULL config options
DirAuthorities, AlternateBridgeAuthority, AlternateDirAuthority,
and FallbackDir.

Add assertion in consider_adding_dir_servers() for checks in
validate_dir_servers():
"You cannot set both DirAuthority and Alternate*Authority."

Only add the default fallback directories when the DirAuthorities,
AlternateDirAuthority, and FallbackDir directory config options
are set to their defaults.

The default fallback directory list is currently empty, this fix will
only change tor's behaviour when it has default fallback directories.

Fixes bug 15642; bugfix on 90f6071d in 0.2.4.7-alpha. Patch by "teor".

When self-testing reachability, use ExtendAllowPrivateAddresses
to determine if local/private addresses imply reachability.

The previous fix used TestingTorNetwork, which implies
ExtendAllowPrivateAddresses, but this excluded rare configs where
ExtendAllowPrivateAddresses is set but TestingTorNetwork is not.

Fixes bug 15771; bugfix on 0.2.6.1-alpha, bug #13924.
Patch by "teor", issue discovered by CJ Ess.

Incidently, this fixes a bug where the maximum value was never used when
only using crypto_rand_int(). For instance this example below in
rendservice.c never gets to INTRO_POINT_LIFETIME_MAX_SECONDS.

  int intro_point_lifetime_seconds =
    INTRO_POINT_LIFETIME_MIN_SECONDS +
    crypto_rand_int(INTRO_POINT_LIFETIME_MAX_SECONDS -
                    INTRO_POINT_LIFETIME_MIN_SECONDS);

Signed-off-by: David Goulet <dgoulet@ev0ke.net>

An introduction point is currently rotated when the amount of INTRODUCE2
cells reached a fixed value of 16384. This makes it pretty easy for an
attacker to inflate that number and observe when the IP rotates which leaks
the popularity of the HS (amount of client that passed through the IP).

This commit makes it a random count between the current value of 16384 and
two times that.

Fixes #15745

Signed-off-by: David Goulet <dgoulet@ev0ke.net>

Till someone writes get_interface_address6 interface enumeration that is
routing table aware, these tests will continue to fail on certain
systems because the get_interface_address6() code is broken.

The alternative has been available since 2007, there's no way to
actually enable the ifdef, and it breaks on well formed but not OpenSSL
style inputs.

Fixes bug 15591; patch from joelanders