Document extension clash.

CHANGES

@@ -8,14 +8,19 @@
     
      Experimental support for encrypt then mac from
      draft-gutmann-tls-encrypt-then-mac-02.txt
-    
+
      To enable it set the appropriate extension number (0x10 for the test
      server) using e.g. -DTLSEXT_TYPE_encrypt_then_mac=0x10
-    
+ 
      For non-compliant peers (i.e. just about everything) this should have no
      effect.
 
      WARNING: EXPERIMENTAL, SUBJECT TO CHANGE.
+
+     NOTE: unfortunately the test server value (0x10) clashes with the draft
+     ALPN extension. Until this is resolved the only way to check against the
+     test server is to temporarily change the ALPN extension value (ugh!).
+
      [Steve Henson]
 
   *) Add callbacks supporting generation and retrieval of supplemental