dpkg-genchanges: Use the checksums files list when building the Files field

This should guarantee that the output order is always the same as the
other Checksum fields, even if debian/files entries change order.

debian/changelog

@@ -63,6 +63,8 @@ dpkg (1.18.0) UNRELEASED; urgency=low
     Suggested by Jose M Calhariz <jose.calhariz@hds.com>. Closes: #783014
   * Fix perl warning in dpkg-genchanges when parsing BY-HAND file entries.
     Regression introduced in dpkg 1.17.7. Closes: #781074
+  * Use the checksums files list order when building the Files field to match
+    the other Checksum fields in dpkg-genchanges.
 
   * Perl modules:
     - Rename and deprecate Dpkg::Gettext _g function with new g_.

scripts/dpkg-genchanges.pl

@@ -496,6 +496,10 @@ for my $file ($dist->get_files()) {
         next if (not ($include & BUILD_ARCH_DEP) and not $arch_all);
     }
     $checksums->add_from_file("$uploadfilesdir/$f", key => $f);
+}
+foreach my $f ($checksums->get_files()) {
+    my $file = $dist->get_file($f);
+
     $fields->{'Files'} .= "\n" . $checksums->get_checksum($f, 'md5') .
 			  ' ' . $checksums->get_size($f) .
 			  " $file->{section} $file->{priority} $f";