pmWiki 2.2.51 upgrade and some addon test

 upgraded to PmWiki 2.2.51 (2013.05.08), added new testing pages Main.TextExtract, Main.TestPowerTools, standalone Main.Addons page for includes @ HomePage and PmwikiKitSetup

Rename page was tested, but there are no pages relating to tests for it.

I have not fully tested that BlogIt works with the upgrade, but I do note that save-draft functionality is working on pages, and so should not be affected.