unset any attributes when deleting files

For users who copy D3DRM.DLL from disc, the file may have been copied with a
read only attribute by default, which is preserved in the copy Rebuilder makes
and prevents Rebuilder from re-copying on subsequent runs. This commit clears
all file attributes before re-copying so that this doesn't happen.

Rebuilder/Rebuilder.cs

@@ -1025,6 +1025,7 @@ namespace Rebuilder
                 for (int i = 0; i < dest_files.Length; i++)
                 {
                     Log("Deleting existing file: " + dest_files[i]);
+                    File.SetAttributes(dest_files[i], FileAttributes.Normal);
                     File.Delete(dest_files[i]);
                 }
             }