Whitespace only in deSugar/MatchLit.lhs
Add a warning for overflowing literals; fixes #7895
Add NegativeLiterals extension

I'd been meaning to do this for some time, but finally got around to it
due to the overflowing literals warning. With that enabled, we were
getting a warning for
    -128 :: Int8
as that is parsed as
    negate (fromInteger 128)
which just happens to do the right thing, as
    negate (fromInteger 128) = negate (-128) = -128
Document the Negative Literals extension
Add -XNegativeLiterals to the flag list
Add a warning for empty enumerations; fixes #7881

We now give a warning about enumerations like [5 .. 3] :: Int8.
Fix Trac #8020.

The solution is to use a different notion of apartness. See
http://research.microsoft.com/en-us/um/people/simonpj/papers/ext-f/axioms-extended.pdf
for the gory details. Some comments are also in Notes [Compatibility]
and [Apartness] in FamInstEnv.
Update to Cabal to allow RoleAnnotations
Implement "roles" into GHC.

Roles are a solution to the GeneralizedNewtypeDeriving type-safety
problem.

Roles were first described in the "Generative type abstraction" paper,
by Stephanie Weirich, Dimitrios Vytiniotis, Simon PJ, and Steve Zdancewic.
The implementation is a little different than that paper. For a quick
primer, check out Note [Roles] in Coercion. Also see
http://ghc.haskell.org/trac/ghc/wiki/Roles
and
http://ghc.haskell.org/trac/ghc/wiki/RolesImplementation
For a more formal treatment, check out docs/core-spec/core-spec.pdf.

This fixes Trac #1496, #4846, #7148.
Refactor checking for GADT-like datacons' return types

This check is somewhat subtle. See Note [Checking GADT return types]
in TcTyClsDecls. The new plan is to check *before* desugaring the type
from HsType to Type. This avoids problems with the pattern-match
in rejigConRes.

As a nice side benefit to this, I discovered that Template Haskell
splices were a little conservative in their treatment of valid data
constructors. (For example, a kind signature in the return type caused
failure.) Now, the TH code uses exactly the same function as the
"real" code, which is nice. See hsTyGetAppHead_maybe in HsTypes.
sync-all : Warn on 'pull' operation if not on master branch.