cmd/pack: use log.SetPrefix to make log calls more compact and consistent Taking my own advice from a review of addr2line.
cmd/pack: use log.SetPrefix to make log calls more compact and consistent
Taking my own advice from a review of addr2line.

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/65950044

pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go