Merge origin/maint-0.2.2 for 6007_strict

This code shouldn't have any effect in 0.2.3, since we already accept
(and handle) data received while we are expecting a renegotiation.
(That's because the 0.2.3.x handshake _does_ have data there instead of
the renegotiation.)

I'm leaving it in anyway, since if it breaks anything, we'll want it
broken in master too so we can find out about it.  I added an XXX023
comment so that we can come back later and fix that.

changes/bug6007

@@ -0,0 +1,5 @@
+  o Major bugfixes (security):
+    - When waiting for a client to renegotiate, don't allow it to add
+      any bytes to the input buffer. This fixes a DoS issue. Fix for
+      bugs 6007 and 5934; bugfix on 0.2.0.20-rc.
+