XML.js : parser may fail in IE8 due to schema fetching and validation

[justb4]

This is an IE8-specific (and possibly more versions) issue. I can provide a PR. When loading a WMS Capabilities document via GeoExt and subsequently via the OpenLayers.Format.WMSCapabilities, the responseText parsing in OpenLayers.Format.XML may fail due to DTD/schema checking, strangely even if the XML is DTD-valid. First observed with GeoServer and a GXP example: http://lib.heron-mc.org/heron/latest/examples/catalognl where Layers are loaded via WMSCapabilities.

Apart from the issue that IE actually fetches the DTD over the network, creating overhead, I think that by default validation should be disabled as is for all other browsers. This can be done via the validateOnParse MS.XMLDOM property in the OpenLayers.Format.XML.read() function. I made a local override and can confirm that the following works.

    .
    .
    var node = OpenLayers.Util.Try(
        OpenLayers.Function.bind((
            function() {
                var xmldom;
                /**
                 * Since we want to be able to call this method on the prototype
                 * itself, this.xmldom may not exist even if in IE.
                 */
                if(window.ActiveXObject && !this.xmldom) {
                    xmldom = new ActiveXObject("Microsoft.XMLDOM");
                } else {
                    xmldom = this.xmldom;

                }
                xmldom.validateOnParse = false; // <======
                xmldom.loadXML(text);
                return xmldom;
            }
        ), this),
        function() {
            return new DOMParser().parseFromString(text, 'text/xml');
        },
        .
        .

A similar implementation was done in OL XMLHttpRequest.js as below.

function fGetDocument(oRequest) {
    var oDocument    = oRequest.responseXML,
        sResponse    = oRequest.responseText;
    // Try parsing responseText
    if (bIE && sResponse && oDocument && !oDocument.documentElement && oRequest.getResponseHeader("Content-Type").match(/[^\/]+\/[^\+]+\+xml/)) {
        oDocument    = new window.ActiveXObject("Microsoft.XMLDOM");
        oDocument.async                = false;
        oDocument.validateOnParse    = false;  // <========
        oDocument.loadXML(sResponse);
    }