Basic support for extracting values of global variables

[mkmks]

No description provided.

[bos]

This doesn't build against LLVM 3.0 because you edited the configure.ac script.

Also, this warning makes me nervous:

LLVM/Core/Instructions.hs:216:1:
    Warning: Pattern match(es) are non-exhaustive
             In an equation for `getValConvArg':
                 Patterns not matched:
                     IDRet _ _
                     IDRetVoid
                     IDBrCond _ _ _
                     IDBrUncond _
                     ...

[mkmks]

I've checked the build against LLVM 3.2 and fixed that warning.

[mkmks]

Also closes #37.

[mkmks]

And #43.

[NathanHowell]

Commits like f7e3108 churn a huge amount of code due to formatting changes. Could you rebase this pull request down to a smaller number of commits against the HEAD and avoid unnecessary formatting changes?