Catch fatal xml/html parsing errors and pass them to callback

Xml parsing is more strict and have more unrecoverable errors like
absence of root element or multiply root elements.

lib/Request.js

@@ -56,10 +56,15 @@ function Request(method, url, params, opts, tries, callback) {
         var parse_mode = opts.parse_as;
         if (parse_mode === 'auto')
             parse_mode = getResponseType(res.headers['content-type']);
-        if (parse_mode === 'xml')
-            document = libxml.parseXml(document, { baseUrl: location.href, huge: true });
-        else
-            document = libxml.parseHtml(document, { baseUrl: location.href, huge: true });
+        try {
+            if (parse_mode === 'xml')
+                document = libxml.parseXml(document, {baseUrl: location.href, huge: true});
+            else
+                document = libxml.parseHtml(document, {baseUrl: location.href, huge: true});
+        } catch (e) {
+          callback('Response ' + parse_mode + ' parsing error: ' + e);
+          return;
+        }
 
         if (document === null) {
             callback('Couldn\'t parse response');

test/get.js

@@ -140,7 +140,7 @@ module.exports.multiple = function (assert) {
     }, 5000);
 }
 
-module.exports.function_url = function (assert) {
+module.exports.xml = function (assert) {
   osmosis.get(url + '/xml-auto')
     .then(function (context, data) {
         assert.equal(context.get('link').text(), 'http://example.com');
@@ -160,6 +160,24 @@ module.exports.function_url = function (assert) {
     });
 };
 
+module.exports.error_xml_parse = function (assert) {
+    var tries = 4;
+
+    osmosis.get(url + '/get')
+    .config('parse_as', 'xml')
+    .config('tries', tries)
+    .error(function (msg) {
+        // Multiply root elements are not allowed
+        if (msg.indexOf('parsing error') > -1) {
+            tries--;
+        }
+    })
+    .done(function () {
+        assert.strictEqual(tries, 0);
+        assert.done();
+    });
+};
+
 module.exports.absentQueryString = function (assert) {
     var found = false;
     osmosis.get(url + '/test-query-string')