Fixes needed in tiger/chap2

1. The import of ErrorMsg.ErrorMsg needs to be removed from Parse/Tiger.lex.
2. ErrorMsg/ErrorMsg.java puts a colon before sayPos, but also starts sayPos with a colon except when it is "0.0". This double colon is presumably unintended. (Either that, or for consistency there should be a double colon also before 0.0.)