merge revision(s) r47327: [Backport #10008]

	* ext/zlib/zlib.c (gzfile_reset): preserve ZSTREAM_FLAG_GZFILE
	  [Bug #10101]

	* test/zlib/test_zlib.rb (test_rewind): test each_byte


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47419 b2dd03c8-39d4-4d8f-98ff-823fe69b080e