NAS driver false autodetecting other GML content that happens to have NAS string in its content

[Even Rouault]

Frank,

I have had an issue with the result of the following WFS query :

http://agismap1.faa.gov/geoserver/ows?service=wfs&version=1.1.0&request=GetFeature&typename=aixm:AirportHeliport_arp&maxfeatures=2

This is recognized by the NAS driver because the NAS string is found in the first bytes of the file, but this is the NAS substring from '<aixm:datasourcecode_id>NASR</aixm:datasourcecode_id>', which has nothing to do with NAS.

Based on the NAS sample I've found in ​http://www.geodatenzentrum.de/gdz1/abgabe/testdaten/vektor/nas_testdaten_peine.zip, I'm going to change the logic in the NAS driver to detect "NAS-Operationen.xsd" instead.

I hope this is correct in all cases, but I haven't found any other NAS dataset, so I let you test&judge whether this is OK.

[Even Rouault]

Fix commited in r20257