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/CSecurityVeNCrypt.cxx b/common/rfb/CSecurityVeNCrypt.cxx
index a15da4a..4a25245 100644
--- a/common/rfb/CSecurityVeNCrypt.cxx
+++ b/common/rfb/CSecurityVeNCrypt.cxx
@@ -191,3 +191,9 @@
   return csecurity->processMsg(cc);
 }
 
+bool CSecurityVeNCrypt::isSecure() const
+{
+  if (csecurity && csecurity->isSecure())
+    return true;
+  return false;
+}