hash.c: move Hash specific functions

	* hash.c (rb_ident_hash): move compare_by_identity specific
  function from st.c.

	* hash.c (rb_ident_hash_new): ditto from thread.c.

	* st.c (st_numhash): remove ruby's Hash specific implementation.

	* thread.c (recursive_list_access): use rb_ident_hash_new().

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@49668 b2dd03c8-39d4-4d8f-98ff-823fe69b080e