some errors in lgReadIndex

``` haskell
let oid   = c'git_index_entry'oid entry
```

there is no **oid** field in git_index_entry struct ( changed to **id** )

``` haskell
if 0 /= flags .&. 2 -- c'GIT_IDXENTRY_REMOVE
```

incorrect. flags contains path length in less 12 bits. this expression excluding entries
with path size 2. for GIT_IDXENTRY_REMOVE see flags_extended
