add interpolation-to-mean to corner padding for image pyramid patchwork; other minor changes.

-- fill corners of padding with interpolation of edge padding (which is in turn already an interpolation from the image edge to the imagenet mean).
-- add .PHONY stitch target to top level makefile for building just libStitchPyramid
-- minor fix to testing makefile: add a -L. to src/stitch_pyramid/build/Makefile
-- update matcaffe.cpp comment with current mkoctfile-based build command (can be used to test building matcaffe under octave)
-- condense str() in featpyramid_common.hpp (str() is for debugging printfs)
-- add a copy of str() in JPEDPyramid.cpp (FIXME: use some common copy?)

mwm