Speed improvements

Assorted speed improvements. 

First one is time measurement of the import process so as to see what affect the changes are having, and the addition of the wp_suspend_cache_invalidation call. Saves no real time, about 3 seconds, max. Cuts down on memory use a bit though.

Second one is changing the single SELECT query to use the post_name instead of the post_title, which is not indexed. Shaves about 12-14 seconds off scanning core/trunk, about a 15% improvement.

Third one is a bit more dangerous, disabling autocommit. This shaves off another 10 seconds for me (10% improvement), but might not be safe in certain environments. Worth discussion though.