Display security state when asking for password

Indicate to the user how secure the transport channel is so they
can avoid entering their password for untrusted sites.
diff --git a/common/rfb/CSecurityStack.cxx b/common/rfb/CSecurityStack.cxx
index cfc60fd..47c3f6d 100644
--- a/common/rfb/CSecurityStack.cxx
+++ b/common/rfb/CSecurityStack.cxx
@@ -63,3 +63,12 @@
 
   return res;
 }
+
+bool CSecurityStack::isSecure() const
+{
+  if (state0 && state0->isSecure())
+    return true;
+  if (state == 1 && state1 && state1->isSecure())
+    return true;
+  return false;
+}