bin/autoupdate.in, bin/ifnames.in, lib/Autom4te/General.pm,
lib/Autom4te/Struct.pm, lib/Autom4te/XFile.pm: Add local variables
so that Emacs setups GNU style for perl-mode and cperl-mode.
first check that the trace cache file is up to date, and then
compare its timestamp with that of the output.
* bin/autom4te.in, bin/autoupdate.in, bin/autoscan.in: Normalize
the preamble. Don't require 5.005 as Autom4te::General does it,
and better yet (use `use', not `require'!).
* lib/Autom4te/Struct.pm: Rename the last occurrences of
Class::Struct as Autom4te::Struct.
* lib/Autom4te/General.pm (File::stat): Use it.
(&mtime): New, export it.
* bin/autom4te.in: Use it.
Declare `$req' is invalid if it is outdated.
Don't declare it valid before saving it if something went wrong.
