Tidy synapse collation code. (#1053)
Tidy synapse collation code. (#1053)

* Tidy synapse collation code.
* Further reduce synapse collation allocations.
halfflat/arbor,eth-cscs/nestmc-proto,halfflat/nestmc-proto,halfflat/arbor,halfflat/arbor,eth-cscs/nestmc-proto,halfflat/arbor,halfflat/arbor,halfflat/nestmc-proto,halfflat/nestmc-proto,eth-cscs/nestmc-proto