Delete TLS streams before deleting the session

The streams depend on the session and can crash the program if they
are removed in the wrong order. Do a general cleanup of the life time
management of the streams.
diff --git a/common/rfb/CSecurityTLS.h b/common/rfb/CSecurityTLS.h
index 6791a4a..0d5f899 100644
--- a/common/rfb/CSecurityTLS.h
+++ b/common/rfb/CSecurityTLS.h
@@ -69,8 +69,9 @@
     bool anon;
 
     char *cafile, *crlfile;
-    rdr::InStream* fis;
-    rdr::OutStream* fos;
+
+    rdr::InStream* tlsis;
+    rdr::OutStream* tlsos;
   };
 }