Emit router families in canonical form

This patch has routers use the same canonicalization logic as
authorities when encoding their family lists.  Additionally, they
now warn if any router in their list is given by nickname, since
that's error-prone.

This patch also adds some long-overdue tests for family formatting.

changes/ticket28266

@@ -3,3 +3,8 @@
       under which microdescriptor entries are encoded in a canonical
       form. This improves their compressibility in transit and on the client.
       Closes ticket 28266; implements proposal 298.
+
+  o Minor features (relay):
+    - When listing relay families, list them in canonical form including the
+      relay's own identity, and try to give a more useful set of warnings.
+      Part of ticket 28266 and proposal 298.