Initialize buff to all zeros.
Allow the option to use no 2nd stage compression with lrzip.
Fix test_archive_write_add_filter_by_name_lrzip test case.
There's some bug in lrzip where small files cannot use 2nd stage
compression.
See http://ck-hack.blogspot.com/2012/03/lrzip-0612.html?showComment=1337356929450#c3154145708572533571