Cleaner exporting code for class names in javascript.

Fixed the nil subclasses which are now outputted as subclasses of JS `null`,
not of `globals.nil`, which was undefined (so it worked as a side effect).

Also, code clearly states when it wants ST name and when JS name
(so there is no `'globals.', stClassName` in exporter methods any more).
Revert "boot.js: better "nil is subclass" message"

This reverts commit 731dad0a1423030c594ad842a861242a7fdaaf6c.
Fixes #1026.

Does  not report for subclasses of nil created purposely, as they use
JS null to denote superclass.

The warning appears only for undefined (fixes loading .js)
and/or nil (fixes importing with missing global).
Recompile to make cli without ProtoObject warning
Merge pull request #1027 from herby/gh-1026

Fixes #1026