Modinfo cleanups. Don't use xopen() if you want to iterate through multiple files. Don't abort if unable to open the file, but return error if it can't map it. (And leak the filehandle.) All modinfo_file() actually uses is the filename, no reason to go through dirtree() for that. Nothing is actually _checking_ the return value of modinfo_file(). Avoid global data outside of toy_union. Make sure extension is at end of file (we can add support for more extensions later).