defer decision whether import used on the right side of import declaration should be considered referenced
Simplify the binder so it does not need to double recurse down constructor parameter nodes.
Merge pull request #1491 from Microsoft/binderDoubleRecurse

Simplify the binder so it does not need to double recurse down constructor parameter nodes.
Simplify how we set container.nextContainer now that we don't double recurse.
Merge pull request #1496 from Microsoft/bindingContainers

Simplify how we set container.nextContainer now that we don't double recurse during binding.
Change check cadence.
Do not pass context flags downward while parsing binding elements.

This prevents an unnecessary allocation, simplifies parsing code, and prevents
an issue where parsing depends on context flags not stored in the final tree.
This is an issue for incremental parsing that can lead to nodes being reused
inappropriately.
Merge pull request #1498 from Microsoft/bindingElementContxt

Do not pass context flags downward while parsing binding elements.
harden 'get import declaration' logic
Merge pull request #1466 from Microsoft/linked_imports

defer decision whether import used on the right side of import declarati...
Merge branch 'master' into sourceFileUpdate
Don't check container invariants.  They don't hold true in incremental scenarios.