Scratch file editor for clojurescrit.net

- "Show/hide file editor" link
- Evaluation of file (Cmd/Ctrl+E) returns error or value of last evaluated form
- User feedback during file evaluation: "Evaluating file..."
- More helpful error messages
- *e works in REPL

See demo at http://arthuredelstein.github.com/clojurescript/web/repl.html