Tweak arch tagging to make build/install-in-place less annoying
Previously, autoconf-created Makefiles and the like would contain
duplicate taglines (unfortunately, autoconf doesn't seem to have a
`strip in generated file' comment mechanism) leading to conflicts, and
installing in place would create unknown directories and copies of
source directories (leading to conflicts with the source directories).
This changeset makes all autoconf-processed files use explicit id-tags
and adds .arch-inventory entries to ignore installation directories.
