v0.23.1: Bug fix for AXFR, TestNet rewards and some optimizations

The following bug fixes have been done on top of v0.23.0:

TCP interface now reuses connections

Connections are now kept alive instead of being eagerly closed,
leading to less jitter in resources allocation.

Reduced memory footprint of future Enrollment

An optimization has been done in the transaction pool,
which will lead to improved performance and decreased memory usage
when an Enrollment referencing a not-yet-externalized stake is received.

Commons payout: Take block interval into account

The commons payout code was not propely taking the block interval into account.
While the value is fixed for CoinNet, it is different for TestNet.

Fixed a crash triggered by mishandling log messages

A newly introduced log message uncovered a bug that happened under rare
circumstances when log messages were being written to a file,
and said bug has now been fixed.

DNS: Use the proper value when transfering CNAME records

The recent implementation of AXFR uncovered a bug in the CNAME record handling,
which provided the wrong value (either replicated or not fully qualified).