Strongly bind security objects to connection object

There is already an implicit connection between them, so let's make
it explicit. This allows easy lookup outside of the processMsg() function.
diff --git a/common/rfb/CSecurityVncAuth.cxx b/common/rfb/CSecurityVncAuth.cxx
index 46463e0..6a87498 100644
--- a/common/rfb/CSecurityVncAuth.cxx
+++ b/common/rfb/CSecurityVncAuth.cxx
@@ -40,7 +40,7 @@
 
 static const int vncAuthChallengeSize = 16;
 
-bool CSecurityVncAuth::processMsg(CConnection* cc)
+bool CSecurityVncAuth::processMsg()
 {
   rdr::InStream* is = cc->getInStream();
   rdr::OutStream* os = cc->getOutStream();