Added file node, Ptex placeholder.
Added file node, Ptex placeholder.

        - Added file node, with placeholder for hypothetical support of
          Ptex in OSL or extended OSL texture(), with PTex filter choice
          support, disabled for now, pending discussion.
        - As of OIIO/OSL RB-1.7, texture() should deal directly with UV
          tiling (UDIM in Mari, Zbrush, Mudbox style), without the need
          for the textureatlas() custom function. The explicit Maya UV
          tiling will not be supported, unless texture() supports it out
          of the box.
        - Missing changing frame extension, sprite support.

Aakash1312/appleseed,est77/appleseed,dictoon/appleseed,dictoon/appleseed,Vertexwahn/appleseed,aytekaman/appleseed,pjessesco/appleseed,Biart95/appleseed,Vertexwahn/appleseed,dictoon/appleseed,appleseedhq/appleseed,gospodnetic/appleseed,aytekaman/appleseed,aiivashchenko/appleseed,pjessesco/appleseed,aytekaman/appleseed,pjessesco/appleseed,dictoon/appleseed,gospodnetic/appleseed,aiivashchenko/appleseed,Vertexwahn/appleseed,glebmish/appleseed,glebmish/appleseed,glebmish/appleseed,Aakash1312/appleseed,Vertexwahn/appleseed,est77/appleseed,Biart95/appleseed,gospodnetic/appleseed,aytekaman/appleseed,Biart95/appleseed,est77/appleseed,appleseedhq/appleseed,luisbarrancos/appleseed,pjessesco/appleseed,dictoon/appleseed,luisbarrancos/appleseed,est77/appleseed,Vertexwahn/appleseed,pjessesco/appleseed,est77/appleseed,glebmish/appleseed,appleseedhq/appleseed,luisbarrancos/appleseed,appleseedhq/appleseed,gospodnetic/appleseed,Aakash1312/appleseed,aytekaman/appleseed,appleseedhq/appleseed,Biart95/appleseed,Aakash1312/appleseed,aiivashchenko/appleseed,glebmish/appleseed,Aakash1312/appleseed,Biart95/appleseed,aiivashchenko/appleseed,luisbarrancos/appleseed,aiivashchenko/appleseed,gospodnetic/appleseed,luisbarrancos/appleseed