Merge pull request #1158 from seven1m/io_autoclose2 #1630

Job	Run time
RuboCop	25s
specs (ubuntu, 3.0.6)	1m 27s
specs (ubuntu, 3.1.4)	1m 32s
specs (ubuntu, 3.2.2)	1m 24s
specs (ubuntu, 3.3.0)	1m 22s
specs (macos, 3.0.6)	1m 25s
specs (macos, 3.1.4)	1m 42s
specs (macos, 3.2.2)	2m 45s
specs (macos, 3.3.0)	1m 9s
specs (windows, 3.0.6)	3m 24s
specs (windows, 3.1.4)	5m 38s
specs (windows, 3.2.2)	4m 29s
specs (windows, 3.3.0)	4m 4s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 26s
	32m 12s

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