Fixed a bug with the JavaScript representation of empty regexps
Appended output to the examples' files [ci skip]
Added NormalizedCollection#onDuplicate() to control how add() behaves on conflict
Updated Test#execJS to use Spidermonkey 17 if available
Synced to 2d904a1b210658fd93c1e7e5e0bb41c3cc41f0e0
Synced to 2d904a1b210658fd93c1e7e5e0bb41c3cc41f0e0