Long pathnames patch

I'm making this MR on behalf of SUSE's Enzo Matsumiya, who did most of the work.

When running recursively, wget will verify the length of the whole URL when saving the files. This will make it overwrite files with truncated names, throwing the "The name is too long, ... trying to shorten" messages. The patch moves the length check code to a separate function and call it from the append_dir_structure() for each path element.