fix broken links

[SVN r16812]

index.htm

@@ -319,15 +319,15 @@
                   and <a href=
                   "libs/smart_ptr/shared_ptr.htm#shared_dynamic_cast">shared_dynamic_cast</a>.</li>
 
-                  <li><a href="libs/preprocessor/doc/index.htm">Preprocessor
+                  <li><a href="libs/preprocessor/doc/index.html">Preprocessor
                   Library</a>: changed macro prefix from BOOST_PREPROCESSOR
                   to BOOST_PP, added support for <a href=
-                  "libs/preprocessor/doc/reference/list_adt.htm">list data
+                  "libs/preprocessor/doc/reference/list_adt.html">list data
                   structure</a> manipulation, added examples, made library
                   ANSI C friendly, added generalized <a href=
-                  "libs/preprocessor/doc/reference/for.htm">repetition</a>
+                  "libs/preprocessor/doc/reference/for.html">repetition</a>
                   and <a href=
-                  "libs/preprocessor/doc/reference/while.htm">iteration</a>
+                  "libs/preprocessor/doc/reference/while.html">iteration</a>
                   primitives, improved reference manual.</li>
 
                   <li><a href="libs/thread/doc/index.html">Threads