Add InputStream#ungetc

Works like IO#ungetc

lib/zip/ioextras/abstract_input_stream.rb

@@ -86,6 +86,10 @@ module Zip
         return @output_buffer.slice!(0...sep_index)
       end
 
+      def ungetc(byte)
+        @output_buffer.prepend(byte.chr)
+      end
+
       def flush
         ret_val        = @output_buffer
         @output_buffer = ''

test/input_stream_test.rb

@@ -157,4 +157,14 @@ class ZipInputStreamTest < MiniTest::Unit::TestCase
     }
   end
 
+  def test_ungetc
+    ::Zip::InputStream.open(TestZipFile::TEST_ZIP2.zip_name) do |zis|
+      zis.get_next_entry
+      first_line = zis.gets.chomp
+      first_line.bytes.reverse.each { |b| zis.ungetc(b) }
+      assert_equal('#!/usr/bin/env ruby', zis.gets.chomp)
+      assert_equal("$VERBOSE =", zis.read(10))
+    end
+  end
+
 end