Instead of using an additional voltage/current array mirroring the main volt/curr,
the upml extension now swaps volt with volt_flux and curr with curr_flux
before and after the main engine updates.
This saves memory and therefore also increases the upml speed.
every extension can either implement the single threaded methods e.g. DoPreVoltageUpdates()
or the multithreading aquivalent method e.g. DoPreVoltageUpdates(int threadID)
Engine_Ext_UPML class is an example for a multithreading extensions
Thorsten Liebig