[namespace.udecl] Add a page break before section.

Partially addresses #4228.

Author: Dawn Perchik

source/declarations.tex

@@ -7640,6 +7640,8 @@
 \indextext{using-directive|)}%
 \indextext{namespaces|)}
 
+\newpage
+
 \rSec1[namespace.udecl]{The \tcode{using} declaration}%
 \indextext{using-declaration|(}