Fixing WMS1.1.1 getcapabilities XML parsing error

A xml prefix (xsi) is missing in the WMS1.1.1 getcapabilities request with INSPIRE activated, causing mapserver to generate XML which cannot pass the libxml2 validation.

Tested manually with the code compiled from master:

```
% xmllint insp_vanilla.xml 1> /dev/null
insp_vanilla.xml:129: namespace error : Namespace prefix xsi for type on MandatoryKeyword is not defined
on:MandatoryKeyword xsi:type='inspire_common:classificationOfSpatialDataService'
                                                                               ^
```

Same generated xml with patched code does not print out the previous validation
error.

This error has been reported on the mailing list, see:
http://lists.osgeo.org/pipermail/mapserver-users/2014-January/075965.html
for more details.