lib9: fix memory leak in p9getwd()         although the comment says it uses libc's getenv, without NOPLAN9DEFINES         it actually uses p9getenv which strdups.
lib9: fix memory leak in p9getwd()
        although the comment says it uses libc's getenv, without NOPLAN9DEFINES
        it actually uses p9getenv which strdups.

R=golang-dev, dave, rsc
CC=golang-dev
http://codereview.appspot.com/6285046

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