* io.c (io_setstrbuf): return true if the buffer is newly created.
* io.c (io_set_read_length): shrink the read buffer if it is a new
object and is too large. [ruby-core:81370] [Bug #13597]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59701 b2dd03c8-39d4-4d8f-98ff-823fe69b080e