added functions current_exception_cast, current_exception_diagnostic_information, various other minor changes, documentation update

[SVN r52236]

doc/motivation.html

@@ -108,7 +108,7 @@ catch( boost::<span class="RenoLink"><a href="exception.html">exception</a></spa
     e <span class="RenoLink"><a href="exception_operator_shl.html">&lt;&lt;</a></span> file_name("foo.txt");
     throw;
     }</pre>
-<p>Finally here is how the handler retreives data from exceptions that derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>:</p>
+<p>Finally here is how the handler retrieves data from exceptions that derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>:</p>
 <pre>catch( io_error &amp; e )
     {
     std::cerr &lt;&lt; "I/O Error!\n";