Merge pull request #1603 from evelikov/reader-filter-vtbl

Reader filter rework - simplification, robustness and deadcode removal

diff --cc libarchive/archive_read_disk_posix.c
Simple merge

diff --cc libarchive/archive_read_disk_windows.c
Simple merge

diff --cc libarchive/archive_read_support_filter_xz.c
Simple merge

diff --cc libarchive/archive_write_disk_posix.c
Simple merge

diff --cc libarchive/archive_write_disk_windows.c
Simple merge