some more hover annots, error msgs, numtree

- synthesizing dummy values for simple arrows
- checking record subtyping in heapSat, rather than equality
- some longer error messages and hover annotations for heapSat, inferring
  instantiations, failed close operations
- ace printing object literals with multiple lines if any of the fields
  requires multiple lines
- experimenting with inferring folds with object literals, but not
  incorporated yet...
- starting to play with SunSpider TreeNode and controlflow-recursive examples