udf1: Add link count
funnel into POSIX file mode_t. FIXME: something needs to be done to merge ISO9660 interfaces and UDF and probably the right thing is to make it look like POSIX. Would be nice if there were a library e.g. from GNU fileutils I could use to help.
Note: udf_get_next() needs to advance file entry info
Note: there are valgrind and free() errors that need going over.