xfce4-session has been patched in git for sometime and no-longer needs the patches called for in the ebuild .. These lines can be safely commented out. the ebuild digest regenerated and all willl build fine .. as xfce4-session version 4.12 has been released when upgrading to version 4.12 the patch lines can be removed from the ebuild as well .. I've been following the xfce-dev / git build for over a year and all seems to work well .. thank you to ssuominen for the robust xfce-*-9999.ebuilds
clarification ..
*** This bug has been marked as a duplicate of bug 541962 ***