Better dune support #62

Job	Run time
Coq integration tests (8.4, 3.6)	43s
Coq integration tests (8.5, 3.6)	57s
Coq integration tests (8.6, 3.6)	52s
Coq integration tests (8.7, 3.6)	53s
Coq integration tests (8.8, 3.6)	46s
Coq integration tests (8.9, 3.6)	48s
Coq integration tests (8.10, 3.6)	50s
Coq integration tests (8.11, 3.6)	53s
Coq integration tests (8.12, 3.6)	53s
Coq integration tests (8.13, 3.6)	59s
Coq integration tests (8.14, 3.6)	57s
Coq integration tests (8.15, 3.6)	1m 1s
Coq integration tests (8.16, 3.6)	57s
Coq integration tests (8.17, 3.6)	58s
Coq integration tests (8.18, 3.6)	1m 2s
Coq integration tests (8.19, 3.6)	59s
Coq integration tests (master, 3.6)	3m 58s
	18m 26s

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