A bunch of updates to mt_tbs.

*Allow prefetches to occur during 1st quantum.
*Remove obsolete base_address mechanism.
*Do not count accesses during preallocation.
*Move when get_next_trans() is called to ensure stats are counted properly.
*Reset self.trans_cycle for threads that run through the trace during preallocation.
	This was causing accesses to never be issued.
*Upated 32mb_loops.yaml example to only use 18 threads.