GnuTLS

- Added GnuTLS discovery, linking.
- Added '+/-tls' indicator to diagnostics command.
- Added libgnutls version number to diagnostics command.
- Renamed wcwidth6.c to wcwidth6.cpp, to eliminate a strange build error.

cmake.h.in

@@ -42,6 +42,9 @@ Override PACKAGE_LANGUAGE, then
 #cmakedefine SOLARIS
 #cmakedefine UNKNOWN
 
+/* Found the GnuTLS library */
+#cmakedefine HAVE_LIBGNUTLS
+
 /* Found the lua library */
 #cmakedefine HAVE_LIBLUA