#90 show last 3 path instead of 2 in bookmark menu item

[asl97]

currently i got lots of bookmark with the name as chapter_num/page, i feel that it would be better if the bookmark show the 3rd path too so that it would be name/chapter_num/page

but i ain't really expecting it to be added upstream, it be great if someone could come up with a patch for me, although i already wrote one but it ain't pretty.