Split archive_read_extract2 from archive_read_extract

Split archive_read_extract2 from archive_read_extract

The function archive_read_extract requires a call to
archive_write_disk_set_standard_lookup but the functions archive_read_extract2
and archive_read_extract_set_progress_callback do not. Therefore, the latter
pair of functions, the internal function __archive_read_get_extract and the
static function copy_data are moved out of archive_read_extract.c into the new
file archive_read_extract2.c.

This ensures that when statically linking, the standard user and group lookup
functions will not be linked into a program unless they are really needed.

Signed-off-by: Paul Barker <paul@paulbarker.me.uk>