tests/helpers-testrepo.sh

manifest: call m1.load and m2.load before writing a subtree

As part of refactoring the manifest, certain test cases started failing because
writesubtrees was called with p1 and p2 manifests that had not been loaded (so
accessing m1._dirs resulted in an empty set). Let's call _load on these before
attempting to access _dirs.

This was caught by tests when future patches were applied.

# The test-repo is a live hg repository which may have evolution
# markers created, e.g. when a ~/.hgrc enabled evolution.
#
# Tests are run using a custom HGRCPATH, which do not
# enable evolution markers by default.
#
# If test-repo includes evolution markers, and we do not
# enable evolution markers, hg will occasionally complain
# when it notices them, which disrupts tests resulting in
# sporadic failures.
#
# Since we aren't performing any write operations on the
# test-repo, there's no harm in telling hg that we support
# evolution markers, which is what the following lines
# for the hgrc file do:
cat >> $HGRCPATH << EOF
[experimental]
evolution=createmarkers
EOF