Previously merely printing an error would cause the golden
file comparison (in 'bash run') to fail, but that is no longer
the case with the new run.go driver.
R=iant
CC=golang-dev
https://golang.org/cl/7310087
but with less precision than hardware counterparts.
fixed a number of tests to output BUG when they failed.
changed the runner to distinghuish between output
and output containing ^BUG
R=rsc
CC=dho, golang-dev
https://golang.org/cl/1778041