PreTransRecordTrees are likely optimizable.
Fix bug in inlineable classes.
Allow aliasing to cross the inlineable class constructor barrier.

Basically, this allows to keep information about constants or
aliasing assigned to fields of an inlineable class, for use with
the instance returned by the constructor.
Lift the restriction on aliasing of InlineableClassBeingConstructed.

The only problem is if it is aliased to a field of itself. Otherwise,
scoping rules will prevent any bad thing from happening.
Add direct support for Long in the IR.

This basically delays the translation of Longs to RuntimeLongs from
the compiler to the desugaring. This brings the following benefits:

* It relieves the compiler from the knowledge of RuntimeLong.
* It makes the IR independent of the implementation of Longs (so we
  may change it in the future in a binary-compatible way).
* It allows the optimizer to reason about Longs, in particular to
  constant-fold them.

This prompted several cleanups in the whole Long implementation:
* Incorporate fromString() directly into j.l.Long.parseLong().
* Since done in desugar, "inline by hand" the methods of the
  companion of RuntimeLong. This basically means call directly
  whatever they were forwarding to.
* Hence, there was no method left in this companion, so I could
  merge RuntimeLongImpl back into it, as it used to be.

The whole thing is much cleaner now.