Minor cleanups to text
Added pairmemcpy()

So that no one is writing to vp->vp_octets

Some still are... i.e. the 3 "network to VP" decoding functions.
But that can be fixed fairly simply, later
Added pairstrcpy()

which copies a 'char const *' to a VALUE_PAIR
Added pairsprintf()

Which prints a format string to the vp_strvalue of a VALUE_PAIR