Copy log path into the mutation log.
Copy log path into the mutation log.

This caused massive confusion.  I was maintaining a reference to
something that was changing and ended up opening a log file called
"invalid."

Change-Id: Ie2601112e354a849d1bd94ecfbd25d621af4574c
Reviewed-on: http://review.couchbase.org/12737
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Tested-by: Dustin Sallings <1c08efb9b3965701be9d700d9a6f481f1ffec3ea@spy.net>

hisundar/ep-engine,daverigby/ep-engine,daverigby/ep-engine,daverigby/kv_engine,owendCB/ep-engine,owendCB/ep-engine,couchbase/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,couchbaselabs/ep-engine,membase/ep-engine,daverigby/kv_engine,hisundar/ep-engine,teligent-ru/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,membase/ep-engine,jimwwalker/ep-engine,teligent-ru/ep-engine,couchbaselabs/ep-engine,sriganes/ep-engine,abhinavdangeti/ep-engine,sriganes/ep-engine,owendCB/ep-engine,sriganes/ep-engine,membase/ep-engine,daverigby/kv_engine,abhinavdangeti/ep-engine,abhinavdangeti/ep-engine,couchbaselabs/ep-engine,couchbase/ep-engine,hisundar/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,couchbase/ep-engine,couchbaselabs/ep-engine,daverigby/ep-engine,couchbaselabs/ep-engine,sriganes/ep-engine,teligent-ru/ep-engine,abhinavdangeti/ep-engine,hisundar/ep-engine,abhinavdangeti/ep-engine,membase/ep-engine,jimwwalker/ep-engine,owendCB/ep-engine