crypto/rand: better panic message for invalid Int argument.
crypto/rand: better panic message for invalid Int argument.

Also document the panic to be consistent with math/rand.

Fixes issue 5187.

R=golang-dev, dave, bradfitz, r
CC=golang-dev
https://codereview.appspot.com/8303043

Committer: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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