timestamp empty pages, and only free them if theyve been idle for at least a second.
timestamp empty pages, and only free them if theyve been idle for at least
a second.

this basically brings back the functionality that was trimmed in r1.53,
except this version uses ticks instead of very slow hardware clock reads.

ok tedu@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars