Warn and ignore the MyFamily setting if BridgeRelay is also set

Roger explains at
  http://archives.seul.org/tor/talk/Nov-2011/msg00209.html :

  "If you list your bridge as part of your family in the relay
  descriptor, then everybody can learn your bridge fingerprint, and
  they can look up your bridge's descriptor (and thus location) at
  the bridge directory authority."

Now, we can't stop relays from listing bridges, but we can warn when
we notice a bridge listing anybody, which might help some.

This fixes bug 4657; it's a fix on 0.2.0.3-alpha, where bridges were
first introduced.

changes/bug4657

@@ -0,0 +1,4 @@
+  o Minor bugfixes:
+    - If the configuration tries to set MyFamily on a bridge, refuse to
+      do so, and warn about the security implications. Fix for bug 4657;
+      bugfix on 0.2.0.3-alpha.