Fix the DiffFlag type
Fix the DiffFlag type

This change makes the underlying type of DiffFlag be uint32 instead of
int. That makes it possible to build on 32-bit systems.

Fixes: #487

libgit2/git2go,pks-t/git2go,clns/git2go,clns/git2go,clns/git2go,pks-t/git2go,libgit2/git2go,libgit2/git2go