As has already been answered by @Pk_, "ma klounkee!" has been identified as meaning "the end of you!" (ie "your death") in Huttese, as it was spoken in Episode 1 during the pod race by the character Sebulba. Spoken in isolation it would appear to be some kind of threat.
The most logical reason for it being added into this already controversial scene is perhaps to try and redress some balance to the arguments.
In the original cut of New Hope, Han shot first. This is seen as an important plot element, as it paints him as a rogue, and the film's arc is something of a redemption story for him. The controversy began when, in an updated edition, this was changed to show that Greedo shot first. It is believed this was done in order to make the character of Han Solo a more inherently moral character, perhaps for a younger audience in more modern times.
Having Greedo issue a verbal threat to Han's life would perhaps give Han a reason to shoot first while still maintaining moral integrity. This could be a "happy medium" between the two previous cuts - one that does not remove Han's instinct to take offensive action but gives him a moral reason to do so.