It happened quietly last week. A sign was painted in big stenciled lettering on top of what used to be the Allston outpost of Somerville's Joshua Tree Bar: "The Bee's Knees Supply Co." To longtime residents of Allston, the opening of the Bee's Knees market and restaurant — which happens to have quality sandwiches, wines and other foods — heralds the Brooklynization (or Somervillization or Southie-ization) of the neighborhood.