ctlog_importer: Make DB commit more frequent

* The original interval was 10000 certificates. Now decreased to
  1000, as it looks like a performance bottleneck after comming
  to the phase when most operations are updates.

ctlog_importer.py

@@ -112,7 +112,7 @@ def main():
                 numredundant = numredundant + 1
             else:
                 raise KeyError('Unknown DB save outcome')
-            if numdomains % 10000 == 0:
+            if numdomains % 1000 == 0:
                 database.commit()
     database.commit()
     logger.info("Gathered %d certificates containing %d domain names: %d new, %d updated, %d redundant, %d invalid",