taskset: make threads aware

taskset: make threads aware

Add a new '-a' option to view/modify the CPU affinity for an entire
group of threads belonging to a given PID.  We create two new
functions, print_affinity() and do_taskset() for code simplification.

Example:

zeus@jilguero:~/src/util-linux/schedutils$ ./taskset -a -p 01 3142
pid 3142's current affinity mask: 2
pid 3142's new affinity mask: 1
pid 3164's current affinity mask: 2
pid 3164's new affinity mask: 1
pid 854's current affinity mask: 2
pid 854's new affinity mask: 1

[kzak@redhat.com: - clean up
                  - move variables to struct taskset]

Signed-off-by: Davidlohr Bueso <dave@gnu.org>
Tested-by: Jonathan Gonzalez <zeus@gnu.org>
Signed-off-by: Karel Zak <kzak@redhat.com>