Use final vals where possible in javalanglib.

This means in all the companions of boxed classes. This
makes the constructors of these companions elideable.

The values Float.MIN_NORMAL and Double.MIN_NORMAL have been
deleted, because there was no way to make them constant
expressions. Since they are final vals anyway in the JDK, they
will be constant-folded by scalac, so there is no need to emit
them in our library.
Lots of optimizations here and there in the library.

Review of all the javalib and the library with optimizations
in mind (and knowing what the optimizer can do).
Merge pull request #1030 from sjrd/opt-javalib

Optimizations in the library and javalib