transform: let users pick local files as source

In some case it's desirable to use a local file as the source of the
transform operation. For example, an upstream file from the same
repository that could be sourced at built time.
Skip dpkg checks on the source file if it does not start with /

Author: bluca

dh_configpackage

@@ -378,9 +378,13 @@ foreach my $package (@{$dh{DOPACKAGES}}) {
     foreach my $line (@transformfiles) {
         my $file = shift @$line;
         my $source;
+        my $source_is_local = 0;
         if (@$line[0] =~ /^</) {
             $source = shift @$line;
             $source =~ s/^<//;
+            if ($source !~ m!^/!) {
+                $source_is_local = 1;
+            }
         } else {
             $source = displace_files_replace_name($package, $file, "");
             if ($source eq $file) {
@@ -395,7 +399,10 @@ foreach my $package (@{$dh{DOPACKAGES}}) {
         #    chmod 0755, $rest;
         #}
 
-        $source = check_file($source);
+        # Let users use local files as input
+        if (! $source_is_local) {
+            $source = check_file($source);
+        }
         my $destdir = dirname("$tmp/$file");
         if (! -d $destdir) {
             doit("install", "-d", $destdir);