49ers likely won’t negotiate with Davis or Boone until they show up

49ers tight end Vernon Davis and guard Alex Boone want new contracts.  They’ve boycotted offseason workouts to make it happen. As Matt Maiocco of CSNBayArea.com points out, that may not be the way to make it happen. The 49ers have created a precedent that they won’t negotiate until a player shows up.  That’s how the…