The `integerGmpInternals` test was disabled in
c774b28f as many of the primitives
tested in that test weren't available yet w/ `integer-gmp2`.

However, most operations have been reimplemented by now, with the
exception of

    recipModInteger  :: Integer -> Integer -> Integer
    gcdExtInteger    :: Integer -> Integer -> (Integer, Integer)
    powModSecInteger :: Integer -> Integer -> Integer -> Integer
    powModInteger    :: Integer -> Integer -> Integer -> Integer
    powInteger       :: Integer -> Word -> Integer

which are still missing, and will (time permitting) be reimplemented
over time.