Rephrase PrecedenceXExpression doc

I decided they’re called -Expression, not -Operation, so the doc should
respect that.
Update NarrowingTransformer for ArithmeticOperation
source-gen: Print warning when expandFile failed

I finally realized why ./alias never worked in NarrowingTransformer –
the non-actual method disturbs the alphabetical order, and there’s no
method before which to place ‘PrecedenceXExpression’ because the way I’m
adding these, the new alias is always the last one in order.
RedHatTransformer: Move transformPrecedenceXExpression

to the alphabetically correct position. (The RedHat return types mess up
source-gen’s attempt at alphabetical order.)

Also changes the return type to JTerm. The RedHat AST doesn’t do the
precedence-via-type-system thing, we don’t need to bother doing it. (For
Precedence10Expression and upwards, the return types would probably have
gotten truly monstrous, and therefore also slow!)
Update BinaryOperation test for ArithmeticOperation
Update BinaryOperation conversion for ArithmeticOperation
Add SetOperation, IntersectionOperation

* IntersectionOperation (RedHat’s IntersectionOp) for `a&b`
* SetOperation (RedHat’s BitwiseOp – that must be some ages-old legacy
  name) as abstract supertype
* Precedence4Expression

The test also contains what I believe is the first actual implementation
of an Editor I’ve written (to un-group an expression). Looks like a
pretty good way to edit an AST to me :)

(Still with workaround for ceylon/ceylon-compiler#1728.)
Add tests for SetOperation, IntersectionOperation backend conversion