Get infinite-scroll to send X-PJAX header.

gistfile1.js

$.infinitescroll.prototype.retrieve = function (pageNum) {
        var instance = this,
	opts = instance.options,
	path = opts.path,
	box, frag, desturl, method, condition,
	pageNum = pageNum || null,
	getPage = (!!pageNum) ? pageNum : opts.state.currPage;
	beginAjax = function infscr_ajax(opts) {
            // increment the URL bit. e.g. /page/3/
	    opts.state.currPage++;
            instance._debug('heading into ajax', path);
	    // if we're dealing with a table we can't use DIVs
            box = $(opts.contentSelector).is('table') ? $('<tbody/>') : $('<div/>');
            desturl = path.join(opts.state.currPage);
            // Use PJAX to load the new part:
            $.ajax({
                // params
                url: desturl,
                dataType: opts.dataType,

                //////////////////////////////////////////////////////////////////////////////////
                data: {_pjax: '.pjax-target'},
                beforeSend: function(xhr){ xhr.setRequestHeader('X-PJAX', 'true') },
                //////////////////////////////////////////////////////////////////////////////////

                complete: function infscr_ajax_callback(jqXHR, textStatus) {
                    condition = (typeof (jqXHR.isResolved) !== 'undefined') ? (jqXHR.isResolved()) : (textStatus === "success" || textStatus === "notmodified");
                    if (condition) {
                        box.append($(jqXHR.responseText).find(opts.itemSelector));
                        instance._loadcallback(box, jqXHR.responseText);
                    } else { instance._error('end'); }
                }
            });
	};
        // for manual triggers, if destroyed, get out of here
        if (opts.state.isDestroyed) {
            this._debug('Instance is destroyed');
            return false;
        };
        // we dont want to fire the ajax multiple times
        opts.state.isDuringAjax = true;

        opts.loading.start.call($(opts.contentSelector)[0],opts);
    };