Zip files may actually store symlinks, and that's represented
as a file with unix flag S_IFLNK and with its data containing
the symlink target name.

The other flags are being supported too. Now that the os package
has the full range of flags in a system agnostic manner, there's
no reason to discard that information.

R=golang-dev, adg, rogpeppe
CC=golang-dev
https://golang.org/cl/5624048