os: Fix test to work on Solaris.
os: Fix test to work on Solaris.

On Solaris /bin is a symlink to /usr/bin, so running "pwd" in
the directory "/bin" prints out "/usr/bin".

R=rsc, r, bradfitz
CC=golang-dev
http://codereview.appspot.com/4559043

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