strtoq() handles a signed value, so any value with the high bit set will
be treated as negative, and be clamped. Fix this by adding a new
getenv_uquad(), analogue to getenv_quad(), which uses strtouq() instead
of strtoq(). getenv_array() needs more work to deal with uint64_t, and
will be fixed later as needed.

Sponsored by: Juniper Networks, Inc.