[PostGIS] #5861: pgtopo_import: add switch to request pre-dropping an existing topology

[PostGIS]

#5861: pgtopo_import: add switch to request pre-dropping an existing topology
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  Reporter:  strk      |      Owner:  strk
      Type:  defect    |     Status:  new
  Priority:  medium    |  Milestone:  PostGIS Fund Me
 Component:  topology  |    Version:  master
Resolution:            |   Keywords:
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Comment (by strk):

 Better to go --drop-topology, as it's a big gun we're providing to shoot
 your foot
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5861#comment:1>
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