refactorings for the module boot process

refactorings for the module boot process

* module/ice-9/boot-9.scm (%app): Bind %app and (%app modules) within
  the nested hierarchy before making (guile).
  (the-root-module): Define to '(%app modules guile) together with
  the-root-module's definition.
  (resolve-module): Define a "phase 2" resolve-module that only works on the
  root module.
  (try-module-autoload): No need for stub definition, as modules.c does
  not reference this binding.
  (resolve-module): Redefine, after modules have been loaded, to
  actually do its job, without any hacks for the pre-boot phase.

  Move up the boot code before the definition of resolve-module's
  helpers.