[Distutils] do-nothing fails

Allow me to confess that the following low-priority bug actually bit me: You can't have packages be an empty list. The build directory does not get created and the installer complains it can't copy the tree. Why might I be running distutils to install "nothing"? The CXX package consists of header files and some C and C++ source files; no python files or extension modules at the moment. I propose to put the source files (needed by a builder of a CXX extension) into PYTHON/etc/CXX. The include files get treated like Numeric's. I can obviously work around this but it is a generally nice idea that end cases work.