People with migraines sometimes seek a chiropractor for help, but a small study suggests that any pain relief they get might be a placebo effect.When researchers pitted real chiropractic manipulation against a "sham" version, they found both were equally likely to ease patients' migraine pain.On the other hand, both tactics worked better than patients' usual pain-relieving medications.Experts in pain management stressed that no firm conclusions should be drawn from one small study.But they also said…