Reject directories with the attribute export-ignore already while
queuing them. This prevents read_tree_recursive() from descending into
them and this avoids write_archive_entry() rejecting them later on,
which queue_or_write_archive_entry() is not prepared for.
Borrow the existing strbuf to build the full path to avoid string
copies and extra allocations; just make sure we restore the original
value before moving on.
Keep checking any other attributes in write_archive_entry() as before,
but avoid checking them twice.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>