setup.py fix if tests/ subdir already exists
setup.py fix if tests/ subdir already exists

low-sky/pyspeckit,e-koch/pyspeckit,vlas-sokolov/pyspeckit,bsipocz/pyspeckit,e-koch/pyspeckit,low-sky/pyspeckit,mikelum/pyspeckit,allisony/pyspeckit,jpinedaf/pyspeckit,keflavich/pyspeckit,bsipocz/pyspeckit,pyspeckit/pyspeckit,dinossimpson/pyspeckit,allisony/pyspeckit,vlas-sokolov/pyspeckit,mikelum/pyspeckit,jpinedaf/pyspeckit,keflavich/pyspeckit-obsolete,dinossimpson/pyspeckit,keflavich/pyspeckit,pyspeckit/pyspeckit