- Added "build-date" object to XBPS_PKGPROPS.
- Added "installed_size" object to XBPS_PKGPROPS.
- Add entries to archive with "./" as prefix to match xbps-src.
- Create binpkg atomically (from caller's perspective) in cwd.
(cherry picked from commit efeae7c346e914bca045ffe44627c18321e45be9)