Re-enable trace stitching.

Thanks to Vyacheslav Egorov.

doc/changes.html

@@ -90,7 +90,7 @@ Please take a look at the commit history for more details.
 </ul></li>
 <li>Improvements to the JIT compiler:
 <ul>
-<li>Add trace stitching (disabled for now).</li>
+<li>Add trace stitching.</li>
 <li>Compile various builtins: <tt>string.char()</tt>, <tt>string.reverse()</tt>, <tt>string.lower()</tt>, <tt>string.upper()</tt>, <tt>string.rep()</tt>, <tt>string.format()</tt>, <tt>table.concat()</tt>, <tt>bit.tohex()</tt>, <tt>getfenv(0)</tt>, <tt>debug.getmetatable()</tt>.</li>
 <li>Compile <tt>string.find()</tt> for fixed string searches (no patterns).</li>
 <li>Compile <tt>BC_TSETM</tt>, e.g. <tt>{1,2,3,f()}</tt>.</li>