BLD: test_perf, set cpu affinity and do a gc collect between vbs, in --head mode
BLD: test_perf, add burn-in, warn if 'affinity' missing, transpose running order in --head
BLD: test_perf, explicitly disable gc for runs, correct help message
BLD: numpy 1.7.0 is on pypi, no need to get it from GH anymore
BLD: more travis.yml cleanup