Fix execute skip

Consider script.sql that has been executed on root and branch by means of `londiste3 root-config.ini execute script.sql`. Subsequent attempts display a warning and execute script.sql on root anyway as follows.

```bash
ruslan@root-host$ londiste3 root-config.ini script.sql
2014-07-16 20:46:44,739 6240 INFO EXECUTE: "script.sql" already applied, skipping
2014-07-16 20:46:44,740 6240 INFO script.sql: executing sql
(more output related to execution of script.sql)
```

This pull request corrects the previous behaviour as follows.

```bash
ruslan@root-host$ londiste3 root-config.ini script.sql
2014-07-16 21:14:44,815 30432 INFO EXECUTE: "script.sql" already applied, skipping
2014-07-16 21:14:44,815 30432 WARNING Skipping execution of 'script.sql'
```