cmd/dist: do not use HEAP_GENERATE_EXCEPTIONS flag
cmd/dist: do not use HEAP_GENERATE_EXCEPTIONS flag

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5650048
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go