FDSNWS: incomplete results for duplicated station metadata in database

[megies]

In case there is an (unintentional) duplication of station metadata in the database (e.g. two StationXML files with same (similar?) content uploaded to the database), a FDSNWS request only returns one set of the duplicated information. This is strange, the FDSNWS should also return a duplicated data set (the duplicated channels show up in the WebGIS with duplicated entries as well).