Add cache to locate_template()
The locate_template() function checks stats the filesystem on every call to find templates. Cache these stats in shared memory.

~> siege -b -t30s -c5 http://wp1.localhost
** SIEGE 2.70
** Preparing 5 concurrent users for battle.
The server is now under siege...
Lifting the server siege..      done.
Transactions:		        2408 hits
Availability:		      100.00 %
Elapsed time:		       29.46 secs
Data transferred:	       19.45 MB
Response time:		        0.06 secs
Transaction rate:	       81.74 trans/sec
Throughput:		        0.66 MB/sec
Concurrency:		        4.99
Successful transactions:        2408
Failed transactions:	           0
Longest transaction:	        0.12
Shortest transaction:	        0.02