refs #544 SERVER-4669 Refactoring
- Collapse QueryOp and QueryOptimizerCursorOp into QueryPlanRunner.
- Move QueryPlanSet::Runner to QueryPlanRunnerQueue.
- Move QueryOptimizerCursorImpl class definition to header file.

Conflicts:

	src/mongo/db/queryoptimizer.cpp
	src/mongo/db/queryoptimizer.h
	src/mongo/db/queryoptimizercursorimpl.cpp
	src/mongo/db/queryoptimizercursorimpl.h
	src/mongo/dbtests/queryoptimizercursortests.cpp
refs #544 Move ElapsedTracker to mongo/util/elapsed_tracker.{h,cpp}.

Conflicts:

	src/mongo/SConscript
	src/mongo/db/clientcursor.h
	src/mongo/db/oplog.cpp
	src/mongo/s/d_migrate.cpp