Function expr_trans_compare

* Inserts explicit comparisons of type 'type' to symbol 'sym' into the * expression 'e'. * * Examples transformations for type == E_UNEQUAL, sym == &symbol_no: * * A -> A!=n * !A -> A=n * A && B -> !(A=n || B=n) * A || B -> !(A=n && B=n) * A && (B || C) -> !(A=n || (B=n && C=n)) * * Allocates and returns a new expression. */