update and output import data after import

This pull request adds new options 'wp_parser_root_import_dir' and 'wp_parser_last_import'. The options will be updated after the import has finished.

The output after the import:
```
Updated option wp_parser_root_import_dir: /srv/www/wp-reference/source-code
Updated option wp_parser_last_import: 1400848186
Updated option wp_parser_imported_wp_version: 3.9.1
Time: 180.3474521637
Queries: 304202
Success: Import complete!
```
It also fixes php notices coming from the import_version() function if WP_DEBUG is set.