io.c: use rb_funcallv

* io.c (rb_io_write): use rb_funcallv() instead of rb_funcall() to get
  rid of unnecessary alloca.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43202 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-10-09

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43203 b2dd03c8-39d4-4d8f-98ff-823fe69b080e