Setting IFS to a newline to pass the environment also stopped the command
line from splitting, so '-f a -f b' went out as a single argument and the two
words 'docker compose' were looked up as one program name. Every real command
was broken; only --dry-run, which prints a string, looked right.
The variables are now exported in a subshell instead of going through env(1),
which keeps values with spaces intact and leaves the command line to normal
word splitting.
The tests only checked what --dry-run printed, which is why they missed it.
spec/unit/compose_spec.sh now asserts the argv that is actually executed, for
both the plugin and the standalone binary.
Yann Autissier
234739e531