Drastically simplified by taking advantage of the "install" command's

Drastically simplified by taking advantage of the "install" command's
new flexibility, specifically the 'root' option.  Now, we just use
"install" to do a fake installation into a temporary directory
(the 'bdist_dir' option, which derives from the 'bdist_base' option of
"bdist"), and then tar/zip up that directory.  This means that dumb
built distributions are now relative to the root directory, rather than
the prefix or exec-prefix; this is probably a feature, but does make
them slightly less flexible.