add --fresh-auto-compile

add --fresh-auto-compile

* doc/ref/api-evaluation.texi (Compilation): Add discussion of
  --fresh-auto-compile.
* doc/ref/scheme-scripts.texi (Invoking Guile): Add --fresh-auto-compile
  option.

* NEWS: Add entry.

* libguile/load.c: Define %fresh-auto-compile.
  (scm_primitive_load_path): Use it here.
  (scm_init_load_should_auto_compile): Init from GUILE_AUTO_COMPILE env
  var, with a value of "fresh".

* module/ice-9/boot-9.scm (load-in-vicinity): Auto-compilation cache is
  stale if %fresh-auto-compile is true.

* module/ice-9/command-line.scm (compile-shell-switches): Parse out
  --fresh-auto-compile.