gc.c (gc_stat_internal): add compatible layer.
From Ruby 2.2, keys of GC.stat are changed [Feature #9924].
To provide compatible layer, GC.stat add a default_proc
(if default_proc of given Hash object is not set).
At first use of this compatible layer of interpreter process,
show a warning message like that:
program: GC.stat[:total_allocated_object]
warning message: "warning: GC.stat keys were changed from Ruby
2.1. In this case, you refer to obsolete total_allocated_object' (new key is total_allocated_objects').
Please check https://bugs.ruby-lang.org/issues/9924
for more information."
Pleaes correct my English message :)
hash.c (rb_hash_set_default_proc): export (in internal).