zlib: GzipReader#rewind preserves ZSTREAM_FLAG_GZFILE

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

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

We must preserve the ZSTREAM_FLAG_GZFILE flag to prevent
zstream_detach_buffer from:

a) returning Qnil and breaking out of the `each_byte' loop
b) yielding a large string to each_byte

Note: the test case in bug report takes a long time.  I found this
bug because I noticed the massive time descrepancy between
`each_byte' and `readbyte' loop before this patch.  With this patch,
`each_byte' and `readbyte' both take very long.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47327 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,10 @@
+Sun Aug 31 08:46:44 2014  Eric Wong  <e@80x24.org>
+
+	* ext/zlib/zlib.c (gzfile_reset): preserve ZSTREAM_FLAG_GZFILE
+	  [Bug #10101]
+
+	* test/zlib/test_zlib.rb (test_rewind): test each_byte
+
 Sat Aug 30 19:22:47 2014  Eric Wong  <e@80x24.org>
 
 	* symbol.c (rb_sym2id): do not return garbage object

ext/zlib/zlib.c

@@ -2293,6 +2293,7 @@ static void
 gzfile_reset(struct gzfile *gz)
 {
     zstream_reset(&gz->z);
+    gz->z.flags |= ZSTREAM_FLAG_GZFILE;
     gz->crc = crc32(0, Z_NULL, 0);
     gz->lineno = 0;
     gz->ungetc = 0;

test/zlib/test_zlib.rb

@@ -695,6 +695,11 @@ if defined? Zlib
           assert_equal("foo", f.read)
           f.rewind
           assert_equal("foo", f.read)
+
+          f.rewind
+          bytes = []
+          f.each_byte { |b| bytes << b }
+          assert_equal "foo".bytes.to_a, bytes, '[Bug #10101]'
         end
         open(t.path, "rb") do |f|
           gz = Zlib::GzipReader.new(f)