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Calls marked with xSnprintf shouldn't fail.
Abort program cleanly if any of them does.

Closes #546.

This involves switching from kvm_open(3) to kvm_openfiles(3). The only
difference is that the latter has saner error reporting (see the man
page for details). We can now fatally report the error rather than just
calling assert(3).

These are never necessary when using the standard library.

this caused htop to show processes as if freebsd kernel was their parent.
on next pass reparenting code took chance to run, and that caused process to jump around.
this fixed behaviour should be the correct one

Fixed reparenting issue. PPID should be updated each refresh as any process can get reparented to either
PID1 or even any other PID (if there are custom reapers in the system).
Similar issue with jails, elevated process can ask kernel to attach itself into any jail at any time,
thus JID and jail name can change each refresh cycle.

Added preliminary attempt at jails support on FreeBSD - JID and JAIL (name) columns, somewhat more correct kernel "thread" detection.

Seems FreeBSD kernel can spawn both kernel processes (what is what htop currently sees) and kernel threads.
For now let's consider kernel processes kernel "threads".

`Process_new_fn` had been renamed to `Process_New` in
d880def0