KAREN FREIFELD A longtime executive for Donald Trump is expected to be sent to New York's notorious Rikers Island jail after being sentenced on Tuesday for helping engineer a 15-year tax fraud scheme at the former president's real estate company. Allen Weisselberg, the Trump Organization's former chief financial officer, pleaded guilty in August, admitting that from 2005 to 2017 he and other executives received bonuses and perks that saved the company and themselves money. Weisselberg is expected to be sentenced to five months behind bars, after paying nearly $2 million in taxes, penalties and interest and testifying at the criminal…