biblatex needs the module etoolbox only included in texlive-latexextra. See http://ctan.org/pkg/biblatex .
*biblatex-2.9a-r1 (04 Dec 2014) 04 Dec 2014; Manuel Rüger <mrueg@gentoo.org> +biblatex-2.9a-r1.ebuild, -biblatex-2.9a.ebuild: Add missing dependency on dev-texlive/texlive-latexextra. Fixes bug #531164.