correction as per Niall

[SVN r23386]

doc/v2/faq.html

@@ -701,7 +701,7 @@ void Export_FXThread()
     functions with <tt>void *</tt> arguments or return values using
     thin wrappers and the <i>opaque pointer</i> facility. E.g.:
     <pre>// Declare the following in each translation unit
-struct void_; // Deliberately do not define
+struct void_ {};
 BOOST_PYTHON_OPAQUE_SPECIALIZED_TYPE_ID(void_);
 
 void *foo(int par1, void *par2);