User FITNESSE_ROOTPATH to determine root path for relative external page references.
Document WikiPage interface somewhat
Save responder can deal with empty commit information
Use FileSystemPage.path to determine where the content is.
Do not rely on parent pages for correct paths.
Move render logic to BaseWikiPage so it can be shared between FilesystemPage and SymbolicPage.
Disconnect TestPage from WikiPage.
We're crossing subsystem borders here.
Move setting page properties to the appropriate page types.