Include only world readable files.

gemfeed.py

@@ -2,6 +2,7 @@ import argparse
 import datetime
 import glob
 import os.path
+import os.stat
 import urllib.parse
 
 from feedgen.feed import FeedGenerator
@@ -13,7 +14,12 @@ def find_files():
         index = "index.{}".format(extension)
         if index in files:
             files.remove(index)
-    return files
+    world_readable = []
+    for filename in files:
+        st = os.stat(filename)
+        if st.st_mode & stat.S_IROTH:
+            world_readable.append(filename)
+    return world_readable
 
 def populate_entry_from_file(filename, base_url, entry):
     url = urljoin(base_url, filename)