Add a Makefile target 'distdocs' that generates the documentation
at 'make dist' time (and does not depend on configure).

This simplifies the makefile dependency structure within the doc/
subdirectories a bit and makes it easier to prevent docs from being
built, by removing the 'dist: distdocs' dependency in the root Makefile.
Copy /etc/hosts to chroot next to resolv.conf for DNS resolution.
Uniformize style and order of displaying file size and md5.
Fix HTML validation errors.