Ensure statistics aggregates are ordered with parameterized first

Fixes bug 1298528

Due to WSME re-ordering of query parameters, in the mixed case
any parameterized aggregates must be specified in the URL first,
prior to any unparameterized aggregates.

Otherwise the aggregate parameter will be associated with the
wrong aggregate function.

Change-Id: Ib2c76d03a4fc91d13074a03caade2c776d2309b3