Convert Boost.Threads documentation to BoostBook format.

[SVN r23301]

doc/src/boost.xml

@@ -679,17 +679,8 @@
       <librarycategory name="category:testing"/>
     </libraryinfo>
   </library>
-
-  <library name="Threads" dirname="thread" html-only="1">
-    <libraryinfo>
-      <author>
-        <firstname>William</firstname>
-        <surname>Kempf</surname>
-      </author>
-      <librarypurpose>Portable C++ multi-threading</librarypurpose>
-      <librarycategory name="category:concurrent"/>
-    </libraryinfo>
-  </library>
+  
+  <xi:include href="../../libs/thread/doc/thread.xml"/>
 
   <library name="Timer" dirname="timer" html-only="1" 
            url="../../libs/timer/index.htm">