tar et al: die if bb_copyfd_size copies less than asked for.

(we have bb_copyfd_exact_size now for that kind of usage)

archival/libunarchive/get_header_tar.c

@@ -251,7 +251,7 @@ char get_header_tar(archive_handle_t *archive_handle)
 	}
 
 	/* Strip trailing '/' in directories */
-	/* Must be done after mode is set as '/' is used to check if its a directory */
+	/* Must be done after mode is set as '/' is used to check if it's a directory */
 	cp = last_char_is(file_header->name, '/');
 
 	if (archive_handle->filter(archive_handle) == EXIT_SUCCESS) {