Use Humpty Dumpty to verify linearity of `Input` and `ParseResult`

[m4rw3r]

Use https://github.com/Manishearth/humpty_dumpty to verify, optional dependency since it only works on nightly.

[m4rw3r]

Used rustc 1.2.0-nightly (8937ec100 2015-06-15) to compile since an old nightly was used to build humpty_dumpty.

Got it to run and process the chomp crate, but it did not manage to actually find anything, even when intentionally dropping Input or ParseResult. Is probably due to generics and the unimplemented parts of humpty_dumpty (generic functions are not supported, seems to extend to functions generic over a parameter to the type which is not allowed to be dropped).