Allow monitoring procfs files

[Ulrich Windl]

When trying to monitor Linux procfs files, there is no error message, but effectively it does not work, because procfs files have a stat size of zero typically. For example:

> ll /proc/sys/kernel/random/boot_id
-r--r--r-- 1 root root 0 Jul  4 16:45 /proc/sys/kernel/random/boot_id

So the actual contents is never inspected. For the example above there is content, however:

> wc /proc/sys/kernel/random/boot_id
1 1 37 /proc/sys/kernel/random/boot_id

So it would be nice to monitor such files for changes (for example).