* gegl/buffer/gegl-sampler.[ch]: (gegl_sampler_get_ptr): added a
function used to prime a linear buffer with all needed samples for
interpolation.
For all the interpolators, removed unneded alpha multiplications
(we're interpolating on premultiplied pixels), also moved linear and
cubic to skip unneeded function calls in innerloop.
* gegl/buffer/gegl-sampler-cubic.c:
* gegl/buffer/gegl-sampler-lanczos.c:
* gegl/buffer/gegl-sampler-linear.c:
* gegl/buffer/gegl-sampler-nearest.c:

svn path=/trunk/; revision=2489