+ for strings, global js object, new Foo() works

* module/language/ecmascript/array.scm (*array-prototype*): Declare the
  constructor.

* module/language/ecmascript/base.scm (pput, pdel): Remove some needless
  checks.
  (new): Move definition of new here, and use the constructor.

* module/language/ecmascript/compile-ghil.scm (compile-ghil): Add a stub
  so that when we load a compiled JS program, we make sure the runtime
  has been booted.

* module/language/ecmascript/function.scm (js-constructor): Export a
  js-constructor method instead of a new method.

* module/language/ecmascript/impl.scm (<js-global-object>): Define a new
  class for the global "this" object, wrapping bindings from the current
  module.
  (init-js-bindings!): Define the dozen or so global properties, in the
  current module.
  (+): Define addition operations for non-numbers. This is efficient
  because the generics are only dispatched if the fast-path fails.

module/language/ecmascript/array.scm

@@ -41,7 +41,8 @@
               (else o))))))
 
 (define *array-prototype* (make <js-object> #:class "Array"
-                                #:value new-array))
+                                #:value new-array
+                                #:constructor new-array))
 
 (hashq-set! *program-wrappers* new-array *array-prototype*)