Dispatches events until the next physical line of data is available from
the stream and return the line as a string
object, including the terminating newline character.
This method fails if it reaches the end of the input (see also
stream->end_of_file.
The constant @nil
is returned if no full line becomes available within timeout
seconds. The granularity of timeout timing is system dependant. If the timeout
is @default,
this method blocks forever.
Asynchronous input handling (using stream->input_message)
is the preferred way of handling process data.
