SPRINGFIELD — Gov. Bruce Rauner signed a measure last week that will pay overdue bills and earn a higher interest rate for state investments. State Treasurer Michael Frerichs said this move will save taxpayers up to $100 million a year.Senate Bill 2858 authorizes Frerichs to pay backlogged bills that have been waiting to be paid by state Comptroller Susana Mendoza for 90 days or longer. The measure allows Frerichs to …