The line that sets PYTHONPATH only sets one directory right now.
Yes, this is intentional. imppy.sh is provided so that you can run the
tests and otherwise fiddle with IMP before installing it.
Probably is more useful with
If you want to add extra paths here, you can set the 'pythonpath' scons
variable (add it to config.py). Alternatively, use 'scons install' to
install IMP in a directory of your choice, then set PYTHONPATH, PATH,
LD_LIBRARY_PATH etc. appropriately.