Fix potential deadlocking usage of subprocess.Popen

Documented, albeit subtle, gotcha of Popen objects is that you should
not feed input to the process if it's possible for the process to get
blocked waiting on stdout/stderr writing.  On linux this is only possible
if stdout/stderr wrote something like more than 64k without finishing consuming
stdin.

Either way, it's an obvious fix w/out any risks; thus sorting it.

See http://docs.python.org/2/library/subprocess.html#subprocess.Popen.kill ; the details are in the doc descriptions for stdin/stdout/stderr (that follow that anchor, specifically).