activity.py: Fix all pyflakes and pep-8 warnings

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
ascii_graph: Fix pep-8 warnings

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
write_sched_switch.py: Fix pyflakes and pep-8 warnings

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
ascii_graph: Improve version check

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Merge pull request #5 from stgraber/master

Some more pyflakes/pep-8 fixes