goinstall: added -a flag to mean "all remote packages"
Fixes #897.

goinstall -a can be used to reinstall all packages after an upgrade
goinstall -a -u can be used to update all package
A history of remote package installs is stored in $GOROOT/goinstall.log

R=rsc, adg
CC=golang-dev
https://golang.org/cl/1947041
3 files changed