A first pass at fixing #2973 - comments are welcome. If everybody is
happy, the next step is to deprecate the existing
rendertiddler(s)/savetiddler(s) commands and replace them in all
examples and tiddlywiki.info files with the new equivalents.
“-do-not-delete” flag for savetiddlers command was introduced in 5.1.10
without consistency with the already implemented “noclean” flag for the
rendertiddlers command