* init/process.c (process_environment): Function to build an
environment table for a job containing built-in variables, those
from the configuration, events and finally the upstart job ones.
(process_environment_add): Helper function for the above that
handles adding a variable to the array; dealing with fetching the
value from init's environment if necessary.
(process_setup_environment): This function now gets dropped in
favour of the new ones.
(process_spawn): Call the new process_environment() function and set
the environ variable directly.
* init/process.h (PROCESS_ENVIRONMENT): Define built-in environment
variables that are always copied from our own environment.
Add prototypes.
* init/tests/test_process.c (test_environment): Check that the
environment is built correctly and that each bit overrides the
right other bit.
(test_environment_add): Check that the array is built correctly.
(test_spawn): Adjust order and values of expected environment
to match what's now set.