os/user : use username as fullname if all else fails (on windows)
os/user : use username as fullname if all else fails (on windows)

Fixes issue 4113.

R=golang-dev, alex.brainman
CC=golang-dev
http://codereview.appspot.com/6545054

Committer: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>

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