globals.js added, used in _st.js
export/compile uses globals
smalltalk.[A-Z] => globals.[A-Z]
Globals are different object than smalltalk.

Though, for backward compatibility, smalltalk inherits
from globals, so reading smalltalk[xxx] still works.
Use globals inside boot.js as well to read classes.
Merge pull request #811 from herby/globals

Globals