Pagecontainer: Do not start a load message timeout if one is already started.
Demos: Navigation PHP redirect: Add two-second delay to both the redirect script and the redirect target to illustrate loader behaviour.
Pagecontainer: Separate emission of non-deprecated "pagecontainerload" from deprecated "pageload", move "pagecontainerload" in front of DOM insertion and page enhancement, and for both events bail if the default has been prevented.
Demos: Navigation PHP redirect: Provide solution based on "pagecontainerload" alone.