When a source from a configured sourcedir cannot be added (e.g. it is a
duplicate of another source), log the error message only on the first
attempt adding the source, until the source is removed and added to a
sourcedir again.
This avoids spamming of the system log with error messages if the
reload sources command is called frequently (e.g. from a DHCP renewal
networking script).
When reloading a modified source from sourcedir which is ordered before
the original source (e.g. maxpoll was decreased), the new source is
added before the original one is removed. If the source is specified by
IP address, the addition fails due to the conflict with the original
source. Sources specified by hostname don't conflict. They are resolved
later (repeatedly if the resolver provides only conflicting addresses).
Split the processing of sorted source lists into two phases, so all
modified sources are removed before they are added again to avoid the
conflict.
Reported-by: Thomas Lange <thomas@corelatus.se>
