Fix str/unicode issue in batch media requests.

Reviewed in http://codereview.appspot.com/5569055/.
diff --git a/apiclient/http.py b/apiclient/http.py
index 4563bd1..c8a8cd4 100644
--- a/apiclient/http.py
+++ b/apiclient/http.py
@@ -513,7 +513,7 @@
     if request.body is None:
       body = body[:-2]
 
-    return status_line + body
+    return status_line.encode('utf-8') + body
 
   def _deserialize_response(self, payload):
     """Convert string into httplib2 response and content.
@@ -650,7 +650,7 @@
     boundary, _ = content.split(None, 1)
 
     # Prepend with a content-type header so FeedParser can handle it.
-    header = 'Content-Type: %s\r\n\r\n' % resp['content-type']
+    header = 'content-type: %s\r\n\r\n' % resp['content-type']
     for_parser = header + content
 
     parser = FeedParser()