fixes #13: actor files can now be named use

scripts/engine.cm

@@ -729,7 +729,7 @@ if (progDir && progDir !== '.') {
 }
   
 var progContent = io.slurp(prog)
-var prog_script = `(function ${cell.args.program.name()}($_) { ${progContent} })`
+var prog_script = `(function ${cell.args.program.name()}_start($_) { ${progContent} })`
 var val = js.eval(cell.args.program, prog_script)($_)
 if (val)
   throw new Error('Program must not return anything');