refmterr extract "values do not match"

[jordwalke]

The following is not extracted:

# Unformatted Error Output:
# File "x/x.re", line 61, characters 36-325:
# Error: Signature mismatch:
#        ...
#        Values do not match:
#          external dataUntyped : t event -> unsafe = "foo"
#        is not included in
#          external dataUntyped : t event -> 'unsafe = "foo"
#        File "x/x.re", line 59, characters 2-68: Expected declaration
#        File "x/x.re", line 69, characters 2-67: Actual declaration