Shortened some text lines in the extent manager.
Removed file_t::is_block_device.
Remove file_size and file_zone_size serializer dynamic config options.
Removed extent zones.
Removed extent_zone_t::end.
Removed extent_zone_t::start.
Made extent_reference_set_t use a std::deque<extent_reference_t>.
Removed extent_reference_set_t type.
Used a std::vector<extent_reference_t> instead of this pointless use of  std::deque.
Made extent_reference_t be passed with moves, not pointers.
Made std::vector<extent_reference_t> be moved around instead of passed by pointer.
Made the extent "free list" instead be a priority queue of extent ids.
Made extent_zone_t::free_extents use a std::vector.
Made import command use hard durability, for the sake of researching performance.
Moved GC_YOUNG_EXTENT configs from config/args.hpp to data_block_manager.cc.
Moved GC ratio settings to log_serializer/config.hpp.
Added serializer_young_extent_queue perfmon.
Merge branch 'sam_perfmon' into sam_extent_reference_move_cleanup

Conflicts:
	src/serializer/log/extent_manager.cc
Merge branch 'sam_extent_reference_move_cleanup' into sam_310
Merge branch 'sam_perfmon' into sam_extent_reference_move_cleanup