Add TestResult::must_fail

Closes #18
Merge pull request #22 from japaric/must-fail

Add TestResult::must_fail
Cargo.lock ain't for libraries.
Merge branch 'master' of github.com:BurntSushi/quickcheck
Box `expand_meta_quickcheck`.

Recent changes to the rust AST mean that ItemModifier takes a trait implementation, and thus `expand_meta_quickcheck` needs to be boxed.
Merge pull request #25 from CaptainHayashi/master

Box `expand_meta_quickcheck`.
More changes to bring up to date with master.
0.1.1