testing: add Verbose() to expose whether -test.v is set     Fixes issue 3350.
testing: add Verbose() to expose whether -test.v is set
    Fixes issue 3350.

R=golang-dev, adg, r, fullung
CC=golang-dev
http://codereview.appspot.com/6445092

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang