* upstart/wire.c (upstart_push_array, upstart_pop_array): Implement
new array functions; note that these use a newer format that allows
us to transmit NULL without needing to limit the size of the array.
* upstart/wire.h: Add prototypes.
* upstart/tests/test_wire.c (test_push_array, test_pop_array):
Test the new array functions.