gc.c: Load GC tuning settings earlier during boot.

* gc.c (ruby_gc_set_params): Accept safe_level argument so GC tuning
  settings can be applied before rb_safe_level() is available.
* internal.h (rb_gc_set_params): ditto.
* ruby.c (process_options): Apply GC tuning early during boot process
  so boot-time allocations can benefit. This also benefits any code
  loaded in via `ruby -r`.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43991 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-12-05

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43992 b2dd03c8-39d4-4d8f-98ff-823fe69b080e