engine: prevent a function call for each store file
Python function calls are not cheap. Instead of calling the function once for
each file in store, we use a dedicated function which filters and yields the
required files.
Differential Revision: https://phab.mercurial-scm.org/D9673
cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=$PYTHON "$RUNTESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF