nicer error message if an xinclude'd file does not exist
after clearing the contents of a file, it was impossible to put new content into it
implement a file rename link at the top of the editor pages
when editing a file, add a link at the top to go to the file's logical parent (i.e. where it would be x:included from)
make file renames smarter by updating/removing/adding the x:include in the parent file