Better dune support #45

Job	Run time
Coq integration tests (8.4, 3.6)	41s
Coq integration tests (8.5, 3.6)	54s
Coq integration tests (8.6, 3.6)	49s
Coq integration tests (8.7, 3.6)	51s
Coq integration tests (8.8, 3.6)	51s
Coq integration tests (8.9, 3.6)	51s
Coq integration tests (8.10, 3.6)	55s
Coq integration tests (8.11, 3.6)	1m 1s
Coq integration tests (8.12, 3.6)	56s
Coq integration tests (8.13, 3.6)	52s
Coq integration tests (8.14, 3.6)	54s
Coq integration tests (8.15, 3.6)	57s
Coq integration tests (8.16, 3.6)	57s
Coq integration tests (8.17, 3.6)	56s
Coq integration tests (8.18, 3.6)	58s
Coq integration tests (8.19, 3.6)	57s
Coq integration tests (master, 3.6)	4m 14s
	18m 34s

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