dns_compare_name() function

Compare the "dotted" name "query" with the encoded name "response" to make sure an answer from the DNS server matches the current dns_table entry (otherwise, answers might arrive late for hostname not on the list any more). For now, this function compares case-insensitive to cope with all kinds of servers. This also means that "dns 0x20 bit encoding" must be checked externally, if we want to implement it. Currently, the request is sent exactly as passed in by he user request.