Restore some code from original version which has been removed accidentally by someone.

src/zc/buildout/download.py

@@ -180,25 +180,27 @@ class Download(object):
         self.logger.info('Downloading %s' % url)
         urllib._urlopener = url_opener
         handle, tmp_path = tempfile.mkstemp(prefix='buildout-')
-
         try:
-            try:
-                if not download_network_cached(self.network_cache, tmp_path,
-                                                            url, self.logger):
-
-                    # Download from original url
-                    tmp_path, headers = urllib.urlretrieve(url, tmp_path)
-                    if not check_md5sum(tmp_path, md5sum):
-                        raise ChecksumError(
-                            'MD5 checksum mismatch downloading %r' % url)
-                    # Upload the file to networkcached.
-                    upload_network_cached(self.network_cache, url,
-                                                         tmp_path, self.logger)
-            finally:
-                os.close(handle)
-        except:
+            if not download_network_cached(self.network_cache, tmp_path,
+                                                        url, self.logger):
+
+                # Download from original url
+                tmp_path, headers = urllib.urlretrieve(url, tmp_path)
+                if not check_md5sum(tmp_path, md5sum):
+                    raise ChecksumError(
+                        'MD5 checksum mismatch downloading %r' % url)
+                # Upload the file to networkcached.
+                upload_network_cached(self.network_cache, url,
+                                                     tmp_path, self.logger)
+        except IOError, e:
+            os.remove(tmp_path)
+            raise zc.buildout.UserError("Error downloading extends for URL "
+                              "%s: %r" % (url, e[1:3]))
+        except Exception, e:
             os.remove(tmp_path)
             raise
+        finally:
+            os.close(handle)
 
         if path:
             shutil.move(tmp_path, path)