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/CConnection.h b/common/rfb/CConnection.h
index e0a000f..e29c033 100644
--- a/common/rfb/CConnection.h
+++ b/common/rfb/CConnection.h
@@ -134,6 +134,8 @@
     // Identities, to determine the unique(ish) name of the server.
     const char* getServerName() const { return serverName.buf; }
 
+    bool isSecure() const { return csecurity ? csecurity->isSecure() : false; }
+
     enum stateEnum {
       RFBSTATE_UNINITIALISED,
       RFBSTATE_PROTOCOL_VERSION,