merge revision(s) r46876: [Backport #10039]

	* io.c (rb_io_initialize): [DOC] fix rdoc of append mode.  it does
	  not move the pointer at open.  [ruby-core:63747] [Bug #10039]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47377 b2dd03c8-39d4-4d8f-98ff-823fe69b080e