Fix some ifdef mess in sysdeps/bsd/procmem.c.
Fix some warnings and implicit references.
Fix subnet display.
Bring a couple of patches from FreeBSD.
This is still not perfect but libgtop2 is now much more robust.
Note that it does not work better than previous in-tree version but it
will give us a better base to fix it.
joint work with jasper@
most patches adapted from NetBSD
fsusage patch from naddy@
ok jasper@