Debra Messing and Brian F. O’Byrne talk about their roles in John Patrick Shanley’s play “Outside Mullingar.” They play Anthony and Rosemary, two introverted misfits. Anthony has spent his entire life on a cattle farm in rural Ireland, which suits him well because he’s painfully shy. His neighbor Rosemary is determined to have him but is watching the years slip away. “Outside Mullingar” is playing at the Samuel J. Friedman Theatre.