Harbaugh: Jonathan Martin has “done an excellent job of getting the job done”

The 49ers’ initial 53-player roster has just seven available offensive linemen — five starters and two backups. One of those reserves is ex-Dolphin Jonathan Martin, who will back up both tackle spots and could also be asked to play guard in a pinch. In a conference call with media on Saturday, 49ers coach Jim Harbaugh…