onepage effect only for subpages

[cmb69]

see http://cmsimpleforum.com/viewtopic.php?f=16&t=8800

[cmb69]

After reconsideration I don't think it would be a good idea to add this to Onepage_XH, because that likely would confuse users ("do I need a special OnePage template?"), would clutter the docs and the code. Instead this should better be solved by another plugin – to keep track I've forwarded to cmb69/toxic_xh#5.