Prepare source code for amalgamation (4/6). * src/smooth/ftgrays.c, src/raster/ftraster.c: Undefine RAS_ARG, RAS_ARGS, RAS_VAR, and RAS_VARS before defining it. * src/smooth/ftgrays.c: s/TRaster/black_TRaster/, s/PRaster/black_PRaster/. * src/raster/ftraster.c: s/TRaster/gray_TRaster/, s/PRaster/gray_PRaster/.