evolve: document the "if not shouldupdate" block I missed the "not" in "if not shouldupdate: ... hg.updaterepo()" and it took a long time for me to realize it's about updating *back* to the original commit (or to its successor). Let's add a comment to maybe help the person not make the same mistake.

test-drop.t
test-inhibit.t
test-simple4server.t
tests/test-simple4server-bundle2.t