Update CompileTrees_CalcRFdist.py

gets rid of the len(rfdist) and len(trees) command in the loop.  Since the len is large, I think this would have slowed down the script.  I have instead made variables called lenrfdist=len(rfdist) and lentrees = len(trees).  That way, I only need to read the lines once in the whole output rather than once every line in >8000 lines.  With the old len(rfdist) and trees, the script took approx 3 hrs on Barcoo with 256 MB RAM, and approx 4.5 hrs on my laptop, with <16 GB RAM.