Ensure starting '/' not missing when translating internal OGC schema location

This fix ensures that the starting '/' is not missing in the schemalocation path when translating internal OGC schema location into external OGC schema location.
When running deegree 3.3.8 on EAP 6.2 (JBoss 7.x), as a compressed WAR, we experiences problems with the translated OGC Schema location. The starting '/' in the path was missing, causing the generated schema to not validate. 
E.g. The schemalocation for "extdBaseTypes.xsd" was printed as "http://schemas.opengis.netgml/3.3/extdBaseTypes.xsd" in the DescribeFeature response.

The code in master is the same for this translation as in tag 3.3.8, hence the pull request on master.