New internal variable names in prologues.
smalltalk -> $vm
globals -> $globals
smalltalk -> $vm, forgotten pieces
$vm -> $core
_st -> $recv
boot.js: vm -> api
Final recompile. Fixes #831.
Merge branch 'master' into gh-831
require('amber/helpers') .vm -> .api

plus use boot.js's .api, not .vm
API-CHANGES.txt updates w/ namechanges
Merge pull request #1089 from amber-smalltalk/gh-831

New names of internal variables.