Broadway Meets PBS on Mercy Street
  Broadway mainstays are happily joining the ranks of many who have successfully segued to television. Mercy Street‘s new cast members now include:   Tony Award-winner and Emmy Award-Nominee BrÃan F. O'Byrne ("Mildred Pierce," "Aquarius") is Allan Pinkerton, head of the Union Intelligence Service, based on the real Pinkerton. Tony Award-winner Patina Miller (Pippin, "Madam Secretary," The [&#…