* Fixes issue with #4504 and importvariable copying
ImportVariables widget was using $tw.utils.extend to copy the
variables from temporary set widgets into itself. However,
$tw.utils.extend does NOT behave like Object.assign. It not only
copies all self-owned variables over, but also all variables
in that object's prototype chain. This led to some redundant copying,
and a problem where some variables might show up more than once
(like transclusion).
Fixed now. importvariables widget does its own copying, since it
can't rely on $tw.utils.extend to do the right job, and it can't
count on Object.assign to be there.
* Added test to prevent reversion of #4504
* Slight corrections to new importvariables test
* Changed importVariable to store its ownvariables
Before, importVariables was creating a setWidget for every single variable it would find in its tiddlers, and it would create a long-ass call tree. Now, instead, it just accumulates the variables in itself.
* Can't use Object.assign
Learned the hardway while working on tw5-relink that Object.assign
doesn't exist in IE11. Using $tw.utils.extend instead.
* Retaining setWidget transclusion flexibility
* One more test to verify mixing sets and macros
The new importvariables widget imports macro/variable definitions from
the specified tiddlers and makes them available to its children.
Allows us to split PageMacros up into separate tiddlers.
We still support loading macros from $:/core/ui/PageMacros to help
people upgrading.
Fixes#644 and #559
