This is motivated by trying to implement a struct delegate stream which performs reference counting in close, in order to close the real stream when the count hits zero. The caching behavior of close-stream is a problem. * stream.c (strm_base_init): Initialize close_result to nil, rather than nao. (strm_base_mark): Don't check close_result for nao. (close_stream): Suppress the call to op->close if close_result has a non-nil value, rather than a value other than nao. * tests/018/close-delegate.tl, * tests/018/close-delegate.expected: New files. * txr.1: Document that only a non-nil return is cached by close-stream.