Do not clear is_bad_exit on sybil.

But do clear is_v2_dir.

Fixes bug 21108 -- bugfix on d95e7c7d67134b9b964d49cf8c2bdbf805a in
0.2.0.13-alpha.

changes/bug21108_029

@@ -0,0 +1,6 @@
+  o Major bugfixes (directory authority):
+    - During voting, when marking a node as a probable sybil, do not
+      clear its BadExit flag: sybils can still be bad in other ways
+      too. (We still clear the other flags.) Fixes bug 21108; bugfix
+      on 0.2.0.13-alpha.
+

src/or/dirserv.c

@@ -2239,7 +2239,7 @@ clear_status_flags_on_sybil(routerstatus_t *rs)
 {
   rs->is_authority = rs->is_exit = rs->is_stable = rs->is_fast =
     rs->is_flagged_running = rs->is_named = rs->is_valid =
-    rs->is_hs_dir = rs->is_possible_guard = rs->is_bad_exit = 0;
+    rs->is_hs_dir = rs->is_v2_dir = rs->is_possible_guard = 0;
   /* FFFF we might want some mechanism to check later on if we
    * missed zeroing any flags: it's easy to add a new flag but
    * forget to add it to this clause. */