Fixes#4082
This version removes selective updating of the tag index, instead completely clearing the index on each update. I'm investigating restoring that optimisation.
The test rig previously used a simplified implementation of shadow tiddlers which broke with the new indexing engine. There was also a problem that made that even if indexers were disabled they were still initialised.
This PR fixes both problems, in preparation for fixing #4082
See discussion at https://groups.google.com/d/msgid/tiddlywiki/526754d5-8786-49cd-aaa1-c77311670116%40googlegroups.com:
The history here is that in v5.1.14 we added an "actions" attribute to the checkbox widget that specified an action string to be specified whenever the state of the checkbox changed. The same action string is executed regardless of whether the checkbox was checked or unchecked.
Then in v5.1.16 we merged https://github.com/Jermolene/TiddlyWiki5/pull/3182 which added the "uncheckactions" attribute. The difference between the two is that the uncheckactions are only executed if the checkbox is unchecked. The main "actions" attribute is executed before any actions in "uncheckactions", which makes it possible to arrange things so that the "actions" attribute sets things to the checked state while the "uncheckactions" attribute overwrites those changes to set things to the unchecked state.
In retrospect, it would have made more sense to have also added a "checkactions" attribute that was executed only if the checkbox was checked. I'll investigate adding it for v5.1.20.
Include = before each number in the Mathematics Operators examples,
so that people get used to seeing that in math examples where dupes
are likely.
Only the Mathematics Operators tiddler really needed to be changed;
the example tiddlers for individual operators were already using =.
Fixes#3979.
