lib/Automake/FileUtils.pm, lib/Automake/Struct.pm: Sync from
Automake as follows:
* lib/Autom4te/Configure_ac.pm (find_configure_ac): Use
`$configure_in' instead of `configure.in', to preserve
directory component.
* doc/make-stds.texi, doc/standards.texi: Update from masters.
* lib/Autom4te/Channels.pm, lib/Autom4te/Configure_ac.pm
* lib/Autom4te/FileUtils.pm, lib/Autom4te/XFile.pm: Update
from masters, so that FileUtils.pm's update_file provide --force
support.
* bin/autoheader.in: Pass $force to update_file so that
config.h.in is always recreated when --force.