Turns out duplicate index files do not need to be stored when usedirs is in
use, just when it's not. Ikiwiki is quite consistent about using page/ when
usedirs is in use. (The only exception is the search plugin, which needs
fixing.)
This also includes significant code cleanup, removal of a incorrect special
case for empty files, and addition of a workaround for a bug in the amazon
perl module.
Joey Hess