Require Validation of SLD ExternalGraphic OnlineResource (#4883)

Onlineresource must validate against "sld_external_graphic" entry of
map->web->validation in order to be taken into account.

added thanks to Regione Toscana - SITA
Fix SDE plugin build (#4887)
Merge pull request #4891 from szekerest/sdefix

Fix SDE plugin build (#4887)
Merge branch 'master' of github.com:mapserver/mapserver into wcs20-extensions
Fixing XML range subset parsing.