Better dune support #63

Job	Run time
Coq integration tests (8.4, 3.6)	45s
Coq integration tests (8.5, 3.6)	51s
Coq integration tests (8.6, 3.6)	57s
Coq integration tests (8.7, 3.6)	57s
Coq integration tests (8.8, 3.6)	49s
Coq integration tests (8.9, 3.6)	49s
Coq integration tests (8.10, 3.6)	58s
Coq integration tests (8.11, 3.6)	1m 0s
Coq integration tests (8.12, 3.6)	1m 0s
Coq integration tests (8.13, 3.6)	58s
Coq integration tests (8.14, 3.6)	56s
Coq integration tests (8.15, 3.6)	57s
Coq integration tests (8.16, 3.6)	56s
Coq integration tests (8.17, 3.6)	56s
Coq integration tests (8.18, 3.6)	57s
Coq integration tests (8.19, 3.6)	58s
Coq integration tests (master, 3.6)	1m 24s
	16m 8s

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