When excluding nodes by country, exclude {??} and {A1} too

This is ticket 7706, reported by "bugcatcher."  The rationale here
is that if somebody says 'ExcludeNodes {tv}', then they probably
don't just want to block definitely Tuvaluan nodes: they also want
to block nodes that have unknown country, since for all they know
such nodes are also in Tuvalu.

This behavior is controlled by a new GeoIPExcludeUnknown autobool
option.  With the default (auto) setting, we exclude ?? and A1 if
any country is excluded.  If the option is 1, we add ?? and A1
unconditionally; if the option is 0, we never add them.

(Right now our geoip file doesn't actually seem to include A1: I'm
including it here in case it comes back.)

This feature only takes effect if you have a GeoIP file.  Otherwise
you'd be excluding every node.

1 files changed, 9 insertions, 0 deletions

diff --git a/changes/feature7706 b/changes/feature7706
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+  o Minor features:
+    - When any country code is listed in ExcludeNodes or
+      ExcludeExitNodes, and we have GeoIP information, also exclude
+      all nodes with unknown countries ({??} and {A1} if
+      present). This behavior is controlled by the new
+      GeoIPExcludeUnknown option: you can make such nodes always
+      excluded with 'GeoIPExcludeUnknown 1', and disable the feature
+      with 'GeoIPExcludeUnknown 0'. Setting 'GeoIPExcludeUnknown auto'
+      gets you the default behavior.  Implements feature 7706.