[repo] make extid2eid work with either a session or a connection
The only place it should matter is for restoring pending_operations in
case of failure. Which is not exercised by the test suite. Here be
dragons.
usr/lib/PY_VERSION/*-packages/cubicweb/server/
usr/lib/PY_VERSION/*-packages/cubicweb/hooks/
usr/lib/PY_VERSION/*-packages/cubicweb/sobjects/
usr/lib/PY_VERSION/*-packages/cubicweb/schemas/
usr/share/cubicweb/migration/