* Path#ensureBlock keeps path context
This ensures that if you're inside an ArrowFunction with an expression body (say, you're on the BooleanLiteral in `() => true`), you don't suddenly lose your path context after inserting a variable.
This is because of 82d8aded8e (diff-9e0668ad44535be897b934e7077ecea5R14). Basically, an innocent `Scope#push` caused my visitor to suddenly stop working. Now, we mutate the Path so it's still in the tree.
* Tests
* Figuring out where to place throw statement
* Restored path argument destructuring
* New approach using comma expressions for assignments
* Moved throwNode into body of forXstatements
* Refactored with helper function and ensureBlock, additional tests for update exprs
* Added exec tests for all violations
* Hoisted helper function for comma expression outside of visitor
* Remove whitespace generation and rely on default printing
Changes to printing:
* Add newline after last empty SwitchCase
* Add newlines around block comments if they are non-flow comments or contain newlines
* Fix a few more fixtures
* Consolidate contiguous var declarations in destructuring transform
Fixes#3081.
* Simplify var node coalescing in es2015-destructuring
* Revert "Simplify var node coalescing in es2015-destructuring"
This reverts commit 15cb373f0726f68225f7080a7ae206a63af174ee.
* More careful condition for var coalescing in es2015-destructuring
