added base() function to the interface of the specialized adaptors

[SVN r21619]

doc/function_output_iterator_eg.rst

@@ -0,0 +1,35 @@
+Example
+.......
+
+::
+
+    struct string_appender
+    {
+	string_appender(std::string& s)
+	    : m_str(&s)
+	{}
+
+	void operator()(const std::string& x) const
+	{
+	    *m_str += x;
+	}
+
+	std::string* m_str;
+    };
+
+    int main(int, char*[])
+    {
+      std::vector<std::string> x;
+      x.push_back("hello");
+      x.push_back(" ");
+      x.push_back("world");
+      x.push_back("!");
+
+      std::string s = "";
+      std::copy(x.begin(), x.end(), 
+		boost::make_function_output_iterator(string_appender(s)));
+
+      std::cout << s << std::endl;
+
+      return 0;
+    }