overwrite mode for edit-config in plist-helper.js

function graftPLIST (doc, xml, selector, mode) {
var obj=plist.parse('<plist>'xml'</plist>');
var node=doc[selector];
if (node&&Array.isArray(node) &&Array.isArray(obj)) {
//temporary fix
      (mode == 'overwrite') ? (node = obj) : (node = node.concat(obj));
for (vari=0; i<node.length; i++) {
for (varj=i+1; j<node.length; ++j) {
if (nodeEqual(node[i], node[j])) { node.splice(j--, 1); }
}
}
doc[selector] =node;
} else {
// plist uses objects for <dict>. If we have two dicts we merge them instead of
// overriding the old one. See CB-6472
if (node&&__.isObject(node) &&__.isObject(obj) &&!__.isDate(node) &&!__.isDate(obj)) { // arrays checked above
__.extend(obj, node);
}
doc[selector] =obj;
}

returntrue;
}