add literal around getcurrent error

Author: chx

language/predefined/closure/getcurrent.xml

@@ -19,7 +19,7 @@
   </para>
   <para>
    This method must be called from within a closure; calling it outside of a
-   closure context will result in Error: Current function is not a closure.
+   closure context will result in <literal>Error: Current function is not a closure.</literal>
   </para>
  </refsect1>