Slight reorganization of containers

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Run in both 2.7 and 3.2 on travis

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
scroll_compressor example doesn't call debug_plots on exception

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>
Fixed copy function so that it uses the derived type not the base type to instantiate the new form

Signed-off-by: Ian Bell <ian.h.bell@gmail.com>