Completed initial coprocess functionality.

run_command_silent_and_set_string_to_stderr() now behaves as expected --
and *OH MY FVCK!NG GODDESS* was that ridiculously arduous to achieve.
Such function probably embodies the most lathered degree of blood and
night-sweat I've yet sacrificed to this lamentable project. (I honestly
query whether it was worth it -- itself lamentable.)