various bugs using localparams with stats.field

StatsComponent has two different code paths for dealing with param parsing depending on wether it's a single node request of a distributed request, which results in two very differnet looking bugs (but in my opinion have the same root cause: bogus local param parsing):

• the documented local params for stats.field don't work on distributed stats requests at all
• per field "calcdistinct" doesn't work if localparms are used on single node request