intern.h: move rb_ary_cat from internal.h
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43015 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
intern.h: move rb_ary_cat from internal.h
is described in README.EXT.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43015 b2dd03c8-39d4-4d8f-98ff-823fe69b080e