As Boston police hackney officials and Democratic National Convention hosts prepare to meet cabbies tomorrow to work out a discount voucher plan, one irate driver is exploring a Federal Election Commission complaint. Cab driver Bill Ford, an independent driver who says he's voted for more Democrats than Republicans, objects to what he considers a forced donation to the Democratic Party. The plan now being discussed would require cabbies working the airport to accept discount vouchers and multiple riders. Estimates on the value of the vouchers have been placed at $10 or more, but cabbies said compared to their regular multiple-rider...