Fix numerous bigs in the FreeBSD backend

* Correct calculation of CPU time.
* Fix a bug on newer versions of FreeBSD where computing the process map leads
to a tight error loop.
* Add support for the new procstat API to obtain the list of open files and
cwd.
* Use kvm_openfiles instead of kvm_open to better handle error messages.
* Split some modules out into non-suid modules.
* Properly determine the number of CPUs.

https://bugzilla.gnome.org/show_bug.cgi?id=605431

sysdeps/freebsd/glibtop_machine.h

@@ -24,6 +24,7 @@
 
 #include <sys/param.h>
 #include <nlist.h>
+#include <limits.h>
 #include <kvm.h>
 #include <sys/dkstat.h>
 #include <time.h>