just force to be non-sticky for now; revisit for speed gains later
Series of minor cleanups

- Make undefined and Object.create be fields that are runtime-dependent: this
  speeds up running under SES because they were the only free variables that
  kept hitting the SES-lookup ceiling
- Forgotten ";" after throw statements in js-ast
- Add a a-seq AExpr to avoid creating unnecessary "var" statements in compiled
  code that are never used
- Remove a-try, which is not used