ZnapZend 0.23.4

• Revised CI recipes to pass on contributor forks #680 -- @jimklimov
• Introduced ZNAPZENDTEST_ZFS_list_max_snapshots in mock t/zfs
  (default 58 for dst, as it was hard-coded since at least 2014,
  adding +2 more to src datasets), to speed up developer testing
  iterations; updated the README.md with suggestions #691 -- @jimklimov
• Revised .gitignore files, Makefile.am and Git tracked content
  to drop files (re-)generated during build from Git and so simplify
  life for developers; those generated files are directly added to
  the distribution tarball now #689 -- @jimklimov