Tweaks for system/pagefaults_by_process

The plugin did not work as is with munin 2.0.6. The follow tweaks appear to get it working again.

1. The vlabel was changed from 'seconds' to 'major page faults.'
2. The script was using ARGV[1] which was throwing a warning. I switched it to ARGV[0] and it appears fixed.

Thanks!

Jesse