make the timeout_add_foo wrappers more consistent.

make the timeout_add_foo wrappers more consistent.

take uint64_t as the arg type for timeout_add_msec and timeout_add_usec
like we do for timeout_add_nsec now.

always calculate ticks using uint64_t, and factor out the range checks
on the resulting ticks value so it's done consistently.

ok claudio@