Extended the hack in docbook.xsl for dealing with nested <part> elements.

It now handles the case of <appendix> children of <part>.


[SVN r40554]

tools/boostbook

@@ -1 +1 @@
-Subproject commit d2d2c4b90a628240ffd496dab10d9d17fed5d404
+Subproject commit ba2b0af02cd3afe9d8bcdae9fbf55c2ddd9b6bf0