This is the first commit in a series to make xbps-create build
reproducable packages.
xbps-create uses nftw(3) to walk through all files. As nftw doesn't
sort files it may happen that the resulting packages will have
different checksums due to differentiating orders of files on
different filesystems.
To solve this issue xbps-create uses xbps_directory_t, which is always
sorted, instead of a simple linked list.
5c18a43c1c