Graceful later_fd fallback if later_api.h is newer than installed later #256

Job	Run time
R-CMD-check / setup	6s
routine / routine	1m 37s
website / pkgdown	2m 0s
R-CMD-check / macOS-latest (4.4.2)	2m 13s
R-CMD-check / windows-latest (devel)	4m 54s
R-CMD-check / windows-latest (4.4.2)	4m 39s
R-CMD-check / windows-latest (4.3)	8m 26s
R-CMD-check / windows-latest (4.2)	7m 22s
R-CMD-check / windows-latest (4.1)	6m 59s
R-CMD-check / windows-latest (3.6)	5m 40s
R-CMD-check / ubuntu-latest (devel)	3m 6s
R-CMD-check / ubuntu-latest (4.4.2)	2m 33s
R-CMD-check / ubuntu-latest (4.3.3)	2m 33s
R-CMD-check / ubuntu-latest (4.2.3)	2m 36s
R-CMD-check / ubuntu-latest (4.1.3)	2m 34s
R-CMD-check / ubuntu-latest (4.0.5)	2m 33s
	59m 51s

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