dev-vcs/hg-git-0.8.0 is incompatible with dev-vcs/mercurial-3.3.3 or later. For example, it will error out on ‘hg status’. The problem is fixed in hg-git-0.8.1 (changeset da01212cd53a). hg-git in the portage tree should be upgraded to hg-git-0.8.1 or later in order to solve the problem. (And maybe hg-git-0.8.0 should depend on <mercurial-3.3.3.)
FWIW, I'm ok with this, sadly I'm at the moment on an internet connection which prohibits SSH access.
Committed, thanks!