Make qa/rpc-tests/ compatible with OSX

Reworked send.sh, so it works properly on my Mac (killall send.sh
doesn't work, because the process name is 'bash' not 'send.sh').
So now send.sh writes a .send.pid file, and invoking it as
send.sh -STOP (as the bitcoind -walletnotify) signals that PID.

qa/rpc-tests/util.sh

@@ -23,7 +23,7 @@ function CreateDataDir {
   echo "rpcuser=rt" >> $CONF
   echo "rpcpassword=rt" >> $CONF
   echo "rpcwait=1" >> $CONF
-  echo "walletnotify=killall -HUP `basename ${SENDANDWAIT}`" >> $CONF
+  echo "walletnotify=${SENDANDWAIT} -STOP" >> $CONF
   shift
   while (( "$#" )); do
       echo $1 >> $CONF