Support UIDs outside of signed non-negative
Support UIDs outside of signed non-negative

UID/GID should mostly be opaque uid_t/gid_t.
Mac OSX appears to have `nobody` of -2/4294967294.

This should fix it.

Bug #111

google/google-authenticator-libpam,google/google-authenticator-libpam,google/google-authenticator-libpam,google/google-authenticator-libpam