Creating and loading a message sequence's returns into sequence local data.
Added a minor extension to a test case to ensure that when returning
a function call, won't call the function multiple times.

Additionally, noticed a bug with actually emitting a call to a
sequence send message.  Essentially, require setting the message send
bit to be atomic with actually making the call.  As such, need to put
parens around ternary.  Otherwise, if return a call to a message send,
can get into trouble:

return msg_send();

Translates to:
  return internal_msg_send_call() if set_msg_send_bit else None
      if 0 in _ret_args_array
      else other stuff

Whereas we want:
  return (internal_msg_send_call() if set_msg_send_bit else None)
      if 0 in _ret_args_array
      else other stuff
Previously, had not been loading sequence local variables declared at
the top of message sequence blocks into the sequence local data
store.  This commit fixes that.
In the previous commit, realized that return variables for message
sequences appear in the global message sequence nodes of the ast.
Therefore, can use the same code path for emitting code for the other
non-argument sequence local data.