Make SmarterCSV thread-safe #442

Job	Run time
test_matrix (ubuntu, 2.5)	27s
test_matrix (ubuntu, 2.6)	22s
test_matrix (ubuntu, 2.7)	33s
test_matrix (ubuntu, 3.0)	16s
test_matrix (ubuntu, 3.1)	18s
test_matrix (ubuntu, 3.2)	15s
test_matrix (ubuntu, 3.3)	14s
test_matrix (ubuntu, head)	18s
test_matrix (ubuntu, truffleruby)	42s
test_matrix (ubuntu, truffleruby-head)	54s
test_matrix (ubuntu, jruby)	56s
test_matrix (ubuntu, jruby-head)	1m 7s
test_matrix (macos, 2.5)	1m 31s
test_matrix (macos, 2.6)	1m 31s
test_matrix (macos, 2.7)	1m 4s
test_matrix (macos, 3.0)	23s
test_matrix (macos, 3.1)	25s
test_matrix (macos, 3.2)	33s
test_matrix (macos, 3.3)	50s
test_matrix (macos, head)	55s
test_matrix (macos, truffleruby)	2m 42s
test_matrix (macos, truffleruby-head)	2m 16s
test_matrix (macos, jruby)	1m 54s
test_matrix (macos, jruby-head)	55s
finish	0s
	21m 21s

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