JJ: Description from the destination commit:

add error for unsupported CS denom

JJ: Description from source commit:
better fix

test/dune

@@ -1,11 +0,0 @@
-(test
- (name test)
- (modules test)
- (libraries mte fmt))
-
-; TODO
-; cram test?
-; gcc -o a.out ./test/signatures.c && ./a.out > a.output
-; rm ./a.out
-; dune exec ./test/test.exe > b.output
-; cmp -l a.output b.output