Log Message:
pkgin: Update to 21.10.0.

Add new pkgin-prefer-gzip option to support the feature listed below, and
activate it by default on what I believe are MACHINE_ARCH that would most
benefit from it - no offence intended ;)

## Version 21.10.0 (2021-10-12)

 * Support building with -DPREFER_GZIP_SUMMARY which will attempt to fetch
   pkg_summary.gz first, useful on slower machines with limited memory.