crypto_pk_cmp_keys does not document its error behaviour
/** Compare the public-key components of a and b. Return -1 if a\<b, 0
* if a==b, and 1 if a\>b.
*/
if (!a || !b)
return -1;
if (!a->key || !b->key)
return -1;
Can we replace these with asserts on 0.2.3.x?