callee_id is a PNValue_id, not a PNFunctionId
callee_id is a PNValue_id, not a PNFunctionId

Though it turns out that for most (all?) pnacl-clang generated pexes,
these values are identical for functions.

binji/pnacl.c,binji/pnacl.c,binji/pnacl.c