Include non-aggregated stats in cursor results

Since WT-2029, statistics cursors copy their data with a call to __wt_stat_*_aggregate. That was ignoring any statistics values flagged with no_aggregate.

This led to failures in MongoDB tests when testing against develop:

https://evergreen.mongodb.com/task/mongodb_mongo_master_linux_64_debug_compile_be9455abf3126d6136c9ce884a01a4a3e4389bc4_15_08_25_01_43_58