Correctly propogate cause of exception

csppfetch/__init__.py

@@ -255,7 +255,7 @@ def download_already_present(state, dst, download_stats, i_own_file):
             logging.info("Assuming I'm not allowed to update the cache and that this is okay.")
     except Exception as e:
         msg = 'Unable to update timestamp on "{0}": {1}'.format(dst, e)
-        raise Exception(msg)
+        raise Exception(msg) from e
 
 HUGE_TIMEOUT=60*60*24*30 # 30 days in seconds
 def download_to_file_no_lock(url, dst, fileobj, timeout=HUGE_TIMEOUT):