Fix asio description.

[SVN r48041]

doc/src/boost.xml

@@ -61,7 +61,7 @@
          <surname>Kohlhoff</surname>
        </author>
 
-       <librarypurpose>Portable networking, including sockets, timers, hostname resolution and socket iostreams.</librarypurpose>
+       <librarypurpose>Portable networking and other low-level I/O, including sockets, timers, hostname resolution, socket iostreams, serial ports, file descriptors and Windows HANDLEs</librarypurpose>
        <librarycategory name="category:io"/>
      </libraryinfo>
    </library>