Generate index.html as the root file name of the documentation set,

Generate index.html as the root file name of the documentation set,
rather than making index.html a symlink to the autogenerated name.
Fixes fatal problems with tar programs that don't handle symlinks
very well (MacOS X).

(The names user.html, admin.html, etc. are still available as make
targets, but they aren't packaged anymore.)

Use the manifest file that the stylesheets generate as the file list
for packaging.  Put graphics in the right place while building, not
while packaging, so you can actually look at them after building.