Turns out the way RDATA limits work is documented after all,
I just didn't search right. The trick to make it work is to
count UPSERTs twice.
This also adds an additional check to ensure TTL changes are
applied on existing records.
For longer records and subtree entries, the deployer created two
separate TXT records. This doesn't work as intended because the client
will receive the two records in arbitrary order. The fix is to encode
longer values as "string1""string2" instead of "string1", "string2".
This encoding creates a single record on AWS Route53.
This change works around the 32k RDATA character limit per change
request and fixes several issues in the deployer which prevented it from
working for our production trees.
