merge revision(s) 44790: [Backport #9472]

	* io.c (rb_io_syswrite): add RB_GC_GUARD
	  [Bug #9472][ruby-core:60407]


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/branches/ruby_2_0_0@44792 b2dd03c8-39d4-4d8f-98ff-823fe69b080e