Interoperability of WIP 'sysinfo' command

Hi there,

I know it's work-in-progress, but I'd like to point out that the current
implementation of the 'sysinfo' command will only work on machines
running some sort of Linux.

Putting aside Windows, POSIX doesn't specify any sort of procfs. This
means that the command won't run on *BSD, Solaris, etc. Maybe one
solution would be to divide the code up into platform-specific parts
(e.g. one function per OS)?

I know that FreeBSD puts system info in a sysctl interface (accessable
through a sysctl(3) system call). Linux implements sysctl(3) as calls to
procfs, maybe use that instead of calling the shell.

Thanks,
Kevin Zheng