minor Makefile fixes/removals to make compilation work under Mac OS X
minor Makefile fixes/removals to make compilation work under Mac OS X

jas14/khmer,kdmurray91/khmer,F1000Research/khmer,ged-lab/khmer,Winterflower/khmer,F1000Research/khmer,jas14/khmer,kdmurray91/khmer,souravsingh/khmer,souravsingh/khmer,F1000Research/khmer,kdmurray91/khmer,Winterflower/khmer,ged-lab/khmer,souravsingh/khmer,ged-lab/khmer,jas14/khmer,Winterflower/khmer