Drift variable guarding

[ptheywood]

The drift member variable is guarded out differently between the implementations.

circles_spatial3D guards out the member variable entirely if the macro is not defined to a non negative integer.

The 3 other implementations do not guard out the member variable.

This should be standardised to make performance comparisons fair, either to keep it on in all or guard it out in all. RTC makes guarding it out more fun.

Additionally, brute force and spatial do not compute the number of messages the same. For fairness of perforamnce benchmarks this should only be tracked if enabled, or bruteforce should perform the unnneccesary increment operator per message, but this will harm performance.