Made aggregation of two stats samples faster
Made aggregation of two stats samples faster

'Adding' two orddicts can be easily done with O(N) instead of
O(N²). Which is what we're doing here.

We're not using orddict:merge because our behavior is to only use keys
that are present in first proplist. So that we don't try to
merge/display stats that are unsupported/unkown on this node.

Badarith case is likely slightly slower (stats_reader may return
undefined in some rare cases), but it's very uncommon.

Change-Id: I0d52a2bac8bb8bc81cbc6fc87306cd5664415ff4
Reviewed-on: http://review.membase.org/6207
Tested-by: Aliaksey Kandratsenka <340b8e09ca65cd3fc686427fcfed17e87eaf61e2@gmail.com>
Tested-by: Dale Harvey <491ccac09a36ad1e38b698f273b84fd8efc31071@arandomurl.com>
Reviewed-by: Dale Harvey <491ccac09a36ad1e38b698f273b84fd8efc31071@arandomurl.com>

nimishzynga/ns_server,mschoch/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,nimishzynga/ns_server,mschoch/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,membase/ns_server,ceejatec/ns_server,nimishzynga/ns_server,daverigby/ns_server,nimishzynga/ns_server,membase/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,vzasade/ns_server,daverigby/ns_server,ceejatec/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,ceejatec/ns_server,membase/ns_server,nimishzynga/ns_server,vzasade/ns_server,t3rm1n4l/ns_server,membase/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,daverigby/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,vzasade/ns_server,vzasade/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,daverigby/ns_server