pushes an rr to an rrset (which really are rr_list's).
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*rr_list: the rrset to push the rr to
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*rr: the rr to push
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Returns true if the push succeeded otherwise false
ldns_rr_set_pop_rr()
pops the last rr from an rrset. This function is there only
for the symmetry.
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rr_list: the rr_list to pop from
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Returns NULL if nothing to pop. Otherwise the popped RR
AUTHOR
The ldns team at NLnet Labs. Which consists out of
Jelte Jansen and Miek Gieben.