cmd/api: make it work even when cgo is disabled make use of $USER or %USERNAME% to determine the current user. Fixes issue 6578.
cmd/api: make it work even when cgo is disabled
make use of $USER or %USERNAME% to determine the current user.
Fixes issue 6578.

R=golang-dev, bradfitz, alex.brainman
CC=golang-dev
https://codereview.appspot.com/14649043

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