+ Upgraded importer to use MySQLi, for compatibility with PHP 5.5+. Man, why do they always have to make it complicated..? (import.php)

- Reverting Pandos's attachmentUploadDir change. I'm not 100% sure, but my latest import test showed that the importer didn't create extra attachment folders, and I don't have time to deal with this right now. Also, 100 messages per round..? Isn't that a bit overkill? Upped it to 250. It's a bit faster and shouldn't be as taxing as 500 per pass, should it..? And why did the RC version stay at 500 anyway..? (smf2_to_wedge.xml, smf2RC_to_wedge.xml)

Signed-off-by: Nao <nao@wedge>