allow claimrewards after 86100 seconds

[cc32d9]

producer_pay.cpp, line 79:

check( ct - prod.last_claim_time > microseconds(useconds_per_day), "already claimed rewards within past day" );

this condition is a source of constant headache because one cannot establish a simple cron job to run every 24 hours. Please make it >= microseconds(useconds_per_day) - 300000000, so that it gives 300 seconds room for possible delays or microforks.

The rewards calculation does not rely on the fact that it's more than 24 hours. it will work fine for shorter periods too.

[deckb]

Moving this to the new reference system contract repo.

https://github.com/EOSIO/eosio.system/tree/v2.0.0-rc1 introduces a change to rewards which may make this issue a non-issue. We should revisit in a bit.