/usr/lib/python2.7/dist-packages/mercurial/sshserver.py is in mercurial-common 2.0.2-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python2.7/dist-packages/mercurial/../../../../share/pyshared/mercurial/sshserver.py