Hack merge of diffusion_2d_old?/ and diffusion_2d/.

diff --git a/src/diffusion_2d_old?/Makefile b/src/diffusion_2d/Makefile
similarity index 100%
rename from src/diffusion_2d_old?/Makefile
rename to src/diffusion_2d/Makefile

diff --git a/src/diffusion_2d_old?/2d_parabolic.c b/src/diffusion_2d/parabolic_2d.c
similarity index 100%
rename from src/diffusion_2d_old?/2d_parabolic.c
rename to src/diffusion_2d/parabolic_2d.c

diff --git a/src/diffusion_2d_old?/2d_source.c b/src/diffusion_2d/source_2d.c.2001
similarity index 100%
rename from src/diffusion_2d_old?/2d_source.c
rename to src/diffusion_2d/source_2d.c.2001