Send a stored block
function _tr_stored_block(buf, // input block
		stored_len, // length of input block
		eof // true if this is the last block for a file
		) {
			send_bits((STORED_BLOCK << 1) + (eof ? 1 : 0), 3); // send block type
			copy_block(buf, stored_len, true); // with header
		}