Grass Valley's school board is expected review a response tonight to allegations that the district's previous superintendent received unauthorized salary increases that should not have been included in the calculations of his retirement compensation.The response comes two months after the grand jury's report about former superintendent Jon Byerrum . Since then, school district staff and board members have remained mum on the matter, indicating only that the district would respond to the allegations by the Sept. 4 deadline set forth by the grand jury.The June 7 report noted that Byerrum, who retired in June 2010, received a nearly $13,000 raise, …