named-xfer using 'generic' source after 'transfer-source' failed

[Peter Koch]

Item 578 in the CHANGES file documents the introduction of a fallback
feature for the 'transfer-source' option (-x in named-xfer.c). Should
the connect fail for the selected address, another attempt is made with
whatever source address the operating system chooses. This behavior is not
documented and BIND9 seems not to act this way.

On nameservers with several thousand slave zones the second attempt just
occupies a precious 'named-xfer' slot without a real chance of fetching
the zone (due to the connect failure and AXFR restrictions at the master, or
even router access lists). The likelihood of a temporary network failure should
be much higher than that of an erroneously chosen source address.
That for the drawbacks, but what are/were the benefits motivating the second
attempt and is there any chance to make this feature disappear or become
optional in 8.2.3-final?

-Peter