#69 Definition of MAX & MIN macro is not correct

[zhiqiang cai]

We need to add the round bracket in the MAX &MIN definition in the "common/include/r_macros.h"

define MAX(a,b) (((b)>(a))?(b):(a))

Or it will cause error such as in the

tls12_prf() {

dgi = MAX(DIG_SHA256, ssl->cs->dig)-0x40;

}

in case ssl->cs->dig = DIG_SHA384 or higher.