Resolv: Multiple strings should be concatenated in a DNS record's data

As per http://tools.ietf.org/html/rfc4408#section-3.1.3, when a TXT or SPF record contains multiple strings, those strings should be concatenated without any delimiter. Resolv was taking the first string, which meant that valid data in a TXT record wouldn't be available. This change just concatenates the strings together.