Only write the new 'LA' experimental extra block if it's explicitly enabled.
Enable it in the appropriate tests.

E.g.,

$ bsdtar cf - --format=zip --option zip:experimental .

The syntax supports multiple experiments;
use --option zip:experiment_la to enable just the 'LA' experiment.
Improve memory management in the large zip test
Change the first field of the 'LA' extra block to the full 'version made by'
Merge branch 'master' of github.com:kientzle/libarchive-zip64