main: initialize 'p' before the try/finally that uses it.

Otherwise, if we fail to run the subprocess, the finally section doesn't
work quite right.

main.py

@@ -116,6 +116,7 @@ def handler(signum, frame):
 signal.signal(signal.SIGINT, handler)
 
 ret = 95
+p = None
 try:
     try:
         p = subprocess.Popen([subpath(subcmd)] + argv[2:],