* Consolidate command-line option processing. Several new options:

* Consolidate command-line option processing.  Several new options:
  -large, -edwin, -library, -option-summary.  Each major option now
  has a two-step default: first an environment variable is checked,
  and if that doesn't exist, a built-in default is used.

  The point of these changes is to permit a Scheme executable program
  to have sufficient flexibility that it can be installed at many
  sites without modification to the built-in defaults.

* Move all option defaults and option specifications to new file
  "option.c".

* New primitive `get-unused-command-line' returns only that part of
  the command line that was left unused by the option-processing code.

* Rename `parent_process_is_emacs' to `option_emacs_subprocess'.

* Move all specialized exit handling to "term.c".

* Move several macro defaults from "default.h" to the files in which
  they are referenced.