Add a .gitignore.
Whitespace.
Support QuickCheck >= 2.7.

Tested with both 2.7.3 and 2.6. Ideally, we would like to use tf-random's fancy
/dev/urandom seed generation, but that would require generalising the seed type
in the library (StdGen uses Int and TFGen uses (Word64, Word64, Word64,
Word64)).
Merge pull request #5 from 23Skidoo/quickcheck-2.7

Support QuickCheck >= 2.7.