gobuilder: prefix the tarball with 'go.', tweak release regexp
gobuilder: prefix the tarball with 'go.', tweak release regexp

R=rsc
CC=golang-dev
http://codereview.appspot.com/3775047

pombredanne/go-deleteme,apparentlymart/golang,h8liu/golang,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,ssrl/go,h8liu/golang,apparentlymart/golang,gnanderson/go,h8liu/golang,tv42/old-go,ssrl/go,dsriram/golang,apparentlymart/golang,tv42/old-go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,h8liu/golang,tv42/old-go,ssrl/go,tv42/old-go,h8liu/golang,gnanderson/go,tv42/old-go,dsriram/golang,gnanderson/go,gnanderson/go,h8liu/golang,ssrl/go,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,ssrl/go,dsriram/golang,pombredanne/go-deleteme,ssrl/go,h8liu/golang,ssrl/go,dsriram/golang,apparentlymart/golang,dsriram/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme