Patch for Debug.QuickCheck

[Isaac Jones]

While we're talking about quickcheck, I noticed that the "vector"
function mentioned in the manual is inconsistent with the one in the libraries:

The manual [1] claims:

Useful Generator Combinators
If g is a generator for type t, then

    * two g generates a pair of ts,
    * three g generates a triple of ts,
    * four g generates a quadruple of ts,
    * vector n g generates a list of n ts. 
...

Whereas the type is actually:
vector :: Arbitrary a => Int -> Gen [a]

BTW, Martin's suggestion (defaultConfig) is useful for when I want to
use "check" to run a particular number of tests (say 200 instead of
the default 100) but I don't want to bother changing the other
sensible values.

peace,

isaac

[1] http://www.math.chalmers.se/~rjmh/QuickCheck/manual.html