Stop quickbook from generating empty <calloutlist>

elements (which is invalid docbook and causes apache fop 0.94 to 
choke and die).


[SVN r40050]

tools/quickbook

@@ -1 +1 @@
-Subproject commit b3289d42238ec8548158ff0cf90c5ae9a7c3720e
+Subproject commit 59d2a41f26c468f67b0c881b43700e83311ecffb