Better dune support #61

Job	Run time
Coq integration tests (8.4, 3.6)	40s
Coq integration tests (8.5, 3.6)	54s
Coq integration tests (8.6, 3.6)	53s
Coq integration tests (8.7, 3.6)	57s
Coq integration tests (8.8, 3.6)	51s
Coq integration tests (8.9, 3.6)	52s
Coq integration tests (8.10, 3.6)	54s
Coq integration tests (8.11, 3.6)	54s
Coq integration tests (8.12, 3.6)	1m 0s
Coq integration tests (8.13, 3.6)	59s
Coq integration tests (8.14, 3.6)	1m 0s
Coq integration tests (8.15, 3.6)	57s
Coq integration tests (8.16, 3.6)	1m 0s
Coq integration tests (8.17, 3.6)	59s
Coq integration tests (8.18, 3.6)	1m 0s
Coq integration tests (8.19, 3.6)	58s
Coq integration tests (master, 3.6)	4m 7s
	18m 55s

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