Make `test_get_current_niceness` query the libc nice value instead of
hard-coding a value of zero. This avoids a spurious failure on systems
which have a non-zero default nice value.
This fixes spurious failures on my machine.
This introduces an argument preprocessing step for the nice tool in
order to support the legacy nice adjustment syntax (`nice -1 foo`,
`nice --1 foo`, `nice -+1 foo` and so forth).
This is a preprocessing step because the interaction between these
arguments and the existing `nice -n -1` syntax becomes context
dependent, in a way that is currently difficult to capture through
clap.
Signed-off-by: Ed Smith <ed.smith@collabora.com>
