updates the comments
better error messages
makes conversion tests more forgiving
Select.qual originals are now attached to quals, not to selects

This is better than the original approach, because it is resistant
to situations when a select is typechecked, then disassembled and reassembled
(e.g. like in the adjusted test).
better handling for constructor invocations
moves supercall ensugaring to host

This was one of the few ensugarings when I hesitated wrt their placement.

On the one hand, representing `B(2)` in `class C extends B(2)` as an Apply
is syntactically natural, even if a bit awkward.

On the other hand, applications of types to terms are particularly incompatible
with scalac's infrastructure (e.g. app.symbol is a type symbol, not a superctor symbol),
and that bit me when I implemented name/default desugaring for supercalls.
Therefore, I'm reverting the original decision to have supercall processed
in ensugar and moving it to host.
moves the list of supported ensugarings to the top of the file
ensugars default getters
ensugars named and default applications
Merge pull request #12 from xeno-by/master

support for names & defaults