gnome-extra/activity-log-manager-0.9.4 depends on the 0.10 slot (don't think anything else does). I've tested gnome-extra/activity-log-manager-0.9.4 against 0.12 and it appeared to work fine. Reproducible: Always
Collision is with: /usr/share/aclocal/vala.m4
Fixed, thanks for reporting. > 23 Aug 2012; Alexandre Rostovtsev <tetromino@gentoo.org> > vala-0.10.4-r2.ebuild, vala-0.12.1-r1.ebuild: > Fix file collision with vala-common (bug #432456, thanks to Travis Hansen).