Implementation for multi-ip master
SQL statements required by multi-ip master
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Check that the domain isn't already served by the new master
Sets d_server to NULL on failed initialization
Merge pull request #1161 from cmouse/gsql-supermaster-dualstack

WIP: Gsql supermaster dualstack
Merge pull request #1162 from cmouse/nullify-webserver-d_server

Sets d_server to NULL on failed initialization