Fix a bug that Stream parser doesn't expand the user-defined entity r…

…eferences for "text"

## Why?
Pull parser expands character references and predefined entity references, but doesn't expand user-defined entity references.

## Change
- text_stream_unnormalize.rb
```
$LOAD_PATH.unshift(File.expand_path("lib"))
require 'rexml/document'
require 'rexml/parsers/sax2parser'
require 'rexml/parsers/pullparser'
require 'rexml/parsers/streamparser'
require 'rexml/streamlistener'

xml = <<EOS
<!DOCTYPE foo [
  <!ENTITY la "1234">
  <!ENTITY lala "--&la;--">
  <!ENTITY lalal "&la;&la;">
]><root><la>&la;</la><lala>&lala;</lala><a>&lt;P&gt; &lt;I&gt; &lt;B&gt; Text &lt;/B&gt; &lt;/I&gt;</a><b>test&#8482;</b></root>
EOS

class StListener
  include REXML::StreamListener

  def text(text)
    puts text
  end
end

puts "REXML(DOM)"
REXML::Document.new(xml).elements.each("/root/*") {|element| puts element.text}

puts ""
puts "REXML(Pull)"
parser = REXML::Parsers::PullParser.new(xml)
while parser.has_next?
  event = parser.pull
  case event.event_type
  when :text
    puts event[1]
  end
end

puts ""
puts "REXML(Stream)"
parser = REXML::Parsers::StreamParser.new(xml, StListener.new).parse

puts ""
puts "REXML(SAX)"
sax = REXML::Parsers::SAX2Parser.new(xml)
sax.listen(:characters) {|x| puts x }
sax.parse
```

## Before (master)
```
$ ruby  text_stream_unnormalize.rb
REXML(DOM)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™

REXML(Pull)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™

REXML(Stream)
&la;           #<= This
&lala;         #<= This
<P> <I> <B> Text </B> </I>
test™

REXML(SAX)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™
```

After(This PR)

```
$ ruby  text_stream_unnormalize.rb
REXML(DOM)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™

REXML(Pull)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™

REXML(Stream)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™

REXML(SAX)
1234
--1234--
<P> <I> <B> Text </B> </I>
test™
```

lib/rexml/parsers/streamparser.rb

@@ -7,6 +7,7 @@ class StreamParser
       def initialize source, listener
         @listener = listener
         @parser = BaseParser.new( source )
+        @entities = {}
       end
 
       def add_listener( listener )
@@ -28,7 +29,7 @@ def parse
           when :end_element
             @listener.tag_end( event[1] )
           when :text
-            unnormalized = @parser.unnormalize( event[1] )
+            unnormalized = @parser.unnormalize( event[1], @entities )
             @listener.text( unnormalized )
           when :processing_instruction
             @listener.instruction( *event[1,2] )
@@ -40,6 +41,7 @@ def parse
           when :comment, :attlistdecl, :cdata, :xmldecl, :elementdecl
             @listener.send( event[0].to_s, *event[1..-1] )
           when :entitydecl, :notationdecl
+            @entities[ event[1] ] = event[2] if event.size == 3
             @listener.send( event[0].to_s, event[1..-1] )
           when :externalentity
             entity_reference = event[1]

test/test_stream.rb

@@ -88,6 +88,25 @@ def entity(content)
       assert_equal(["ISOLat2"], listener.entities)
     end
 
+    def test_entity_replacement
+      source = '<!DOCTYPE foo [
+      <!ENTITY la "1234">
+      <!ENTITY lala "--&la;--">
+      <!ENTITY lalal "&la;&la;">
+      ]><a><la>&la;</la><lala>&lala;</lala></a>'
+
+      listener = MyListener.new
+      class << listener
+        attr_accessor :text_values
+        def text(text)
+          @text_values << text
+        end
+      end
+      listener.text_values = []
+      REXML::Document.parse_stream(source, listener)
+      assert_equal(["1234", "--1234--"], listener.text_values)
+    end
+
     def test_characters_predefined_entities
       source = '<root><a>&lt;P&gt; &lt;I&gt; &lt;B&gt; Text &lt;/B&gt;  &lt;/I&gt;</a></root>'