Latest app-text/docbook-xsl-stylesheets ebuild version is 1.78.0-r1. Upstream released 1.78.1. Renaming the ebuild is enough. Please bump the ebuild. By the way the HOMEPAGE="http://wiki.docbook.org/topic/DocBookXslStylesheets" is wrong. Correct one is "http://wiki.docbook.org/DocBookXslStylesheets".
1.79.0 is already in the tree, I have fixed the HOMEPAGE var.