* ext/zlib/zlib.c (rb_gzreader_initialize): revert a part of r33937.
	  1st, to change the mode of an IO is very sensitive problem, so
	  the maintainer of this library should judge it.
	  2nd, usually Zlib::GzReader.new is not called directly.  #initialize
	  is called via .open, and in the method the I/O is opened in binary
	  mode, so there is no problem without changing the mode in #initialize.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34544 b2dd03c8-39d4-4d8f-98ff-823fe69b080e