better behaved Rintegral_cst #515

Job	Run time
coq	1m 2s
mathcomp	1m 1s
mathcomp-classical	3m 1s
mathcomp-analysis-single	17m 57s
mathcomp-reals	2m 20s
mathcomp-reals-stdlib	3m 2s
mathcomp-experimental-reals	3m 27s
mathcomp-analysis	16m 32s
mathcomp-analysis-stdlib	15m 44s
ssprove	21m 5s
	1h 25m 11s

Provide feedback