unix_apply.c: separate creation, data extraction, and metadata passes

unix_apply.c: separate creation, data extraction, and metadata passes

This will be needed to support applying extended attributes.  To make
the xattr support more scalable, each file's xattrs will be stored in a
dedicated stream rather than directly in the metadata resource.
Therefore, a file's xattrs might come up for extraction before the
file's contents; so we must create the files first.  We also can't apply
metadata, e.g.  the file mode, before setting xattrs, since the file
mode might indicate the file is readonly, which prevents setting xattrs.
So we must apply metadata last.

Symlinks with xattrs will have to be treated specially as they cannot be
created first.